In 1991, Mercedes-Benz put a V12 in a sedan for the first time in company history and somehow failed to generate much noise about it. The 600 SEL arrived as the flagship of the all-new W140 S-Class: heavy, hulking, and built to a standard of engineering seriousness that the broader market wouldn't fully appreciate until the successor arrived and proved how far things could fall. Thirty-five years later, it remains one of the most technically accomplished luxury sedans ever assembled, and it can still be bought for the price of a used midsize truck.That window is closing.The W140's relationship with the collector world has always been complicated by its own excellence. Too common to be truly rare, too involved to maintain cheaply, and too firmly wedged between the beloved W126 and the later AMG-era flagships to attract passionate tribal loyalty. But the V12 variant, badged 600 SEL from launch in 1991 through June 1993 and later renamed S600, is a different conversation. And that conversation is getting louder among the gearheads paying attention. The Engine Mercedes Had Been Holding Back Bring A Trailer The M120 wasn't just a new powerplant; it was the first V12 engine Mercedes-Benz had ever fitted to a production car. Six liters of naturally aspirated displacement, 394 horsepower, 48 valves, and a character that made nearly 5,000 pounds feel considerably lighter than anything on the scale suggested. At its release, Mercedes called it the most high-tech powerplant the company had ever produced. That wasn't marketing copy.Twin-cam heads and sophisticated electronic fuel management were tuned for seamless torque delivery rather than peak-number theatrics, meaning the M120 pulled from idle with an almost unsettling composure. The result was 0-60 in 6.3 seconds and a governed top speed of 155 mph, numbers that were impressive in 1991 once you accounted for the car's mass and mission.But the M120's bloodline runs further than most owners realize. Pagani fitted the original 6.0-liter version into the Zonda C12, then worked with AMG to stretch the architecture to 7.0 and 7.3 liters for successive Zonda variants. A derived M297 anchored the CLK GTR's FIA GT Championship campaign in 1997, with 25 road-going CLK GTRs delivered in 1999 using an enlarged 6.9-liter version. The engine conceived for a luxury sedan became the foundation of some of the most serious racing and road-going hardware of the late 1990s. The 600 SEL got there first. Overengineered And Proud of It Bring A Trailer The W140's development story includes a detail worth sitting with: early prototypes were sent back to the engineering team for being too small. The car was redesigned to be larger. What emerged measured 205.2 inches long, 74.3 inches wide, and 57.7 inches tall, tipping the scales at just under 5,000 pounds.The pillars were thick. The doors moved like bank vaults and sounded exactly like bank vaults closing. Double-pane window glazing handled noise isolation before door seals or cabin insulation even entered the equation. A heating system that continued circulating warm air after the engine was switched off meant the W140's cabin didn't abruptly abandon its occupants on cold mornings. Self-closing doors and trunk lid, electric windows that reversed when they sensed an obstruction, rear parking markers that deployed from the rear fenders on approach. These weren't features. They were engineering positions.The W140 earned its reputation as the last overengineered Mercedes-Benz because of details exactly like these. Every system that could be made more thorough was. The cost of building to that standard was substantial, and Mercedes priced the car accordingly. That price became the problem. How the W140 Lost the Room Bring A Trailer The 300SE — the base W140, not the V12 — started at $71,500 in 1992. The Lexus LS400 started at $44,300. The Infiniti Q45 at $43,600. Japanese luxury had just proven it could deliver a serene, capable flagship for significantly less money, and a lot of purchase intent that would have gone to Stuttgart went to Tokyo instead. Not because the Mercedes-Benz was outclassed, but because the gap was hard to ignore for buyers without deep brand allegiance.The 600 SEL shared the segment with the BMW 750iL, the Jaguar XJ12, and the Bentley Flying Spur, all serious machines chasing the same buyer. But the W140's engineering brief was different in kind. The problem was that kind costs money, and the pricing reality worked against it in a market suddenly aware of alternatives.Bring A Trailer The real reputational blow came later. The W220, which replaced the W140 in 1998 after an 89-month production run, arrived lighter and cheaper to build, and it quickly earned a reputation for early reliability problems that followed it for years. Enthusiasts began calling the W140 the last true S-Class, and that framing stuck. In hindsight, the 600 SEL's engineering conservatism looked less like excess and more like the correct answer to a question the industry was no longer willing to ask. The Collector Math Is Shifting Bring A Trailer So how does a car with that engineering pedigree end up worth less than a well-optioned pickup truck? It doesn't, for much longer.For most of the 2010s, W140 S600s were available at prices that reflected age and deferred maintenance rather than heritage. That era is ending. The Classic Valuer currently records the average W140 S600 at approximately £16,154 (abount $21,550) in average condition, placing it among the cheapest 30 to 40 percent of all collector cars in their database. Auction aggregator data puts the average transaction closer to $33,652, with the lowest recorded sale sitting at $2,750 for a worn 1995 example as recently as April 2025. The spread is still wide, and that spread is exactly what rewards buyers who know what they're looking at.Bring A Trailer The V12 matters here. Within the W140 family, the S600 carries the highest appreciation potential, tracking above the S500 and S420 variants. Buyers chasing factory V12 flagship provenance are already paying attention, and the pool of clean, properly maintained, unmodified examples is not growing. Cars are aging out of the neglect tier and into the preservation tier, and the gap between a tired survivor and a properly cared-for example is widening faster than the market is pricing it. What Ownership Actually Looks Like Bring A Trailer The W140 S600 is not a trouble-free proposition. Known problem areas include the infrared remote locking system, climate control electronics, and seat adjustment mechanisms, all of which have aged poorly. The automatic transmission's torque converter is a watch item, as are the front axle ball joints and bushings and the hydraulic power-steering hoses. Rust forms at wheel wells, sills, and door bottom edges; on any candidate, check those areas before you look at anything else.The enthusiast community around the W140 has organized meaningfully over the past decade. Specialized independent shops, active forums, and a global pool of owners who treat these cars with the seriousness they deserve have improved parts access considerably. Budget honestly (this is a complex European V12 flagship from the 1990s, not a Japanese compact) and the W140 generally delivers on the engineering promise the factory made.Bring A Trailer Pull one of those vault-weight doors shut and the outside world stops. The double-pane glass, the massive structure, the engine sitting quietly ahead: it all works together exactly as designed. The 600 SEL was built without compromise, and the clean survivors drive without apology. Enthusiasts who track factory V12 lineage deserve to have one in the conversation before the rest of the market catches up.The 600 SEL spent thirty years in the wrong chapter of the collector narrative: too practical to be rare, too involved to be cheap, and too serious for casual appreciation. That's changing. The window on affordable, sorted examples is a real thing right now, and it won't stay open indefinitely. Watch the prices, watch the best-condition cars disappear first, and act accordingly.Sources: The Classic Valuer, Auto-data, Classic.com, Mb140.school