1997 MERCEDES-BENZ S600

Typical onset: 80,000-150,000 mi

Symptoms: Random misfires across multiple cylinders, Rough idle that comes and goes, Check engine light with multiple stored codes, Fuel smell in engine bay from cracked injector harness

Fix: Complete engine harness replacement is the only real fix. Mercedes used biodegradable insulation that turns to dust. Expect 18-25 hours labor to pull both harnesses (engine and injector). Aftermarket improved harnesses available. Do NOT attempt repairs—the insulation contaminates everything it touches.

Estimated cost: $3,500-5,500

Typical onset: 100,000-180,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Rough running on one bank, Milky oil or oil in coolant reservoir

Fix: The M120 is an interference engine—overheating often warps heads. Both heads must come off (30-40 hours), get machined, and receive new gaskets. While you're in there, do valve stem seals, timing chain guides, and water pump. This is why you see so many 'engine rebuild' entries—once heads are off, smart owners go further.

Estimated cost: $6,000-9,000

Typical onset: 90,000-140,000 mi

Symptoms: Transmission fluid in coolant or vice versa (pink milkshake in radiator), Harsh shifts or delayed engagement, Visible transmission sag on driver side, Clunking on acceleration from stop

Fix: The 722.633 transmission cooler lives inside the radiator and fails, cross-contaminating fluids—this kills transmissions. Mounts fail from age and V12 torque. Replace cooler/radiator as unit (6-8 hours), flush both systems multiple times. Mounts are 3-4 hours each. Do both sides preventatively.

Estimated cost: $1,800-3,200

Typical onset: 70,000-120,000 mi

Symptoms: Rough or surging idle, Hesitation on light throttle, Intermittent limp mode, Idle hunts between 500-1000 RPM

Fix: The mechanical linkage between throttle actuators wears at pivot points. Both throttle bodies (one per bank) need linkage service or replacement. 4-6 hours labor. OE parts only—aftermarket fails quickly. Often misdiagnosed as MAF or idle control issues.

Estimated cost: $1,200-2,000

Typical onset: 100,000-150,000 mi

Symptoms: Car sits low on one corner overnight, ABC warning light with 'Drive carefully' message, Hydraulic fluid leaks under car, Harsh ride or excessive body roll

Fix: Active Body Control is brilliant until it isn't. Struts, pump, and accumulator all fail. Front struts are 8-10 hours each, rears 6-8. Pump is 12-15 hours (under engine). Once one component fails, system stress accelerates other failures. Budget $3K-8K depending on what lets go. ABC fluid is special—$50/liter.

Estimated cost: $3,000-8,000

Typical onset: 60,000-120,000 mi

Symptoms: Doors won't soft-close or pop back open, HVAC blend doors stuck or clicking, Cruise control inoperative, Central locking issues

Fix: The W140 uses vacuum for everything. Lines get brittle, check valves fail, reservoirs crack. Diagnosis takes longer than repair—smoke test is essential (3-5 hours total with repairs). Most common: door actuators ($200-400 each) and main supply line from pump.

Estimated cost: $800-1,800