1993 MERCEDES-BENZ S500 W140

Typical onset: 80,000-150,000 mi

Symptoms: Random misfires and rough idle that move between cylinders, Check engine light with multiple cylinder misfire codes, Insulation literally crumbling off wires in engine bay, Fuel smell from cracked injector harness

Fix: Complete engine harness replacement required, not a repair job. 12-16 hours labor to remove intake manifolds, pull old harness, install new one, and sort out all connectors. Mercedes used biodegradable insulation from 1992-1995 that turns to dust.

Estimated cost: $3,500-5,500

Typical onset: 100,000-180,000 mi

Symptoms: Transmission fluid leaking near radiator or under bell housing, Pink or red fluid mixing with coolant in expansion tank, Sudden loss of forward gears after coolant contamination, Overheating transmission and engine simultaneously

Fix: Steel lines rust through where they pass under engine. If coolant mixes with ATF before you catch it, transmission is done. Line replacement is 6-8 hours, but if trans is contaminated add full rebuild or replacement at 18-25 hours.

Estimated cost: $800-1,200 lines only, $4,500-7,000 with transmission replacement

Typical onset: 120,000-200,000 mi

Symptoms: Coolant loss with no visible external leaks, White smoke on cold start that clears, Misfires that seem like head gasket failure, Coolant in valley between cylinder banks

Fix: Often the harness issue causes overheating that actually blows head gaskets, or corroded temp sensors give false readings leading to real overheats. True head gasket job is 18-22 hours on the M119 with both heads off for machining. Many shops misdiagnose and you pay twice—once for harness, then for actual gaskets.

Estimated cost: $4,500-6,500

Typical onset: 80,000-140,000 mi

Symptoms: Heavy clunk when shifting from park to drive or reverse, Vibration at idle in gear that smooths out in neutral, Visible engine movement when revving in park, Transmission tunnel heat because mount lets exhaust sit too close

Fix: Hydraulic mounts leak fluid and collapse. Front and rear engine mounts plus transmission mount should all be done together. 4-6 hours labor with subframe support required.

Estimated cost: $1,200-1,800

Typical onset: 60,000-120,000 mi

Symptoms: Oil smell from engine bay especially when hot, Oil pooling in spark plug wells causing misfires, Visible oil weeping down sides of engine, Smoke from oil burning off exhaust manifolds

Fix: M119 has 8 spark plug tube seals that harden and leak oil into wells. Valve cover gaskets are cork and always seep. Both valve covers with tube seals is 5-7 hours because of the intake plenum removal required.

Estimated cost: $1,200-1,800

Typical onset: 90,000-160,000 mi

Symptoms: Rear end sags when parked overnight, Pump runs constantly or for extended periods, Harsh ride quality over bumps, SLS warning light on dash

Fix: Rear suspension uses hydraulic accumulators that fail internally. Pump works overtime and burns out. Each rear sphere is 2 hours, pump is another 3-4 hours. Many owners delete system for coil conversion to avoid ongoing costs.

Estimated cost: $1,800-2,800 to repair, $1,200-1,500 for coil conversion

Symptoms: AC loses refrigerant with no visible underhood leaks, Musty smell from vents, Oily residue on passenger carpet, System needs recharge every season

Fix: Evaporator is behind the entire dashboard. Full dash removal required, 16-20 hours labor. The W140 dash is notoriously complex to remove. This is the job that totals otherwise good cars because labor exceeds value.

Estimated cost: $3,000-4,500