1999 MERCEDES-BENZ S600

Typical onset: 80,000-120,000 mi

Symptoms: Random misfires across multiple cylinders, Check engine light with 20+ stored fault codes, Rough idle and stumbling, Fuel trim errors, Insulation literally crumbling off wires in engine valley

Fix: Complete engine harness replacement requires upper engine disassembly, coil pack removal, and meticulous rewiring. Mercedes used soy-based insulation that deteriorates. 18-24 labor hours if you catch it early; can cascade into requiring new coil packs, plugs, and ECU repairs if shorts damage modules.

Estimated cost: $4,500-7,500

Typical onset: 90,000-140,000 mi

Symptoms: ABC warning light with car sagging to one corner, Hydraulic fluid leaks pooling under car, Rough ride with suspension bottoming out, Inability to raise vehicle from parked position, Groaning noises from front struts

Fix: The ABC pump, pulsation damper, and hydraulic struts all fail. Pump failure is 8-10 hours, struts are 4-6 hours each corner. Most cars need multiple components by 120k. The pulsation damper ($1,200 part alone) commonly ruptures. Once one component fails, contaminated fluid kills others quickly.

Estimated cost: $3,500-9,000

Typical onset: 100,000-150,000 mi

Symptoms: Metallic knocking from engine bay, Oil consumption exceeding 1 quart per 500 miles, Metal shavings in oil filter, Loss of compression in one or more cylinders, Catastrophic failure with rod through block in worst cases

Fix: The M137 suffers from inadequate oiling to cylinder walls and piston scuffing, especially cylinders 1-3 and 10-12. Requires complete engine-out rebuild: pistons, rings, bearings, machine work, gaskets. 40-60 labor hours minimum. Many owners opt for used engine swap (20-25 hours) due to core complexity.

Estimated cost: $12,000-22,000

Typical onset: 70,000-110,000 mi

Symptoms: Transmission slipping when cold, Pink fluid leaking near radiator area, Harsh shifts or delayed engagement, Clunking when shifting from Park to Drive, Vibration at idle in gear

Fix: The 5-speed 722.6 transmission cooler develops pinhole leaks, contaminating coolant with ATF. Transmission mounts collapse, causing excessive drivetrain movement. Cooler replacement is 4-6 hours (radiator-out job), mounts are 3-4 hours. Often done together. Must flush coolant system thoroughly after cooler leak.

Estimated cost: $1,800-3,200

Typical onset: 80,000-130,000 mi

Symptoms: Vehicle sitting low after being parked overnight, Compressor running constantly, Suspension warning light, Uneven ride height side-to-side, Hissing sounds from wheel wells

Fix: Non-ABC S600s have Airmatic which also fails predictably. Compressor burns out from overwork (6-8 hours), air struts leak at bellows (3-4 hours per corner). Valve block in trunk also leaks. Once compressor struggles, it damages the relay module ($800 part). Replace all four struts together or face repeated failures.

Estimated cost: $2,500-5,500

Typical onset: 120,000+ mi

Symptoms: Hard starting or extended cranking, Loss of power under acceleration, Rough running after fillup, Fuel pump whine or buzzing, Multiple fuel injector failures

Fix: The plastic fuel tank liner degrades, releasing debris that clogs filters and kills injectors/pumps. Requires tank removal and cleaning or replacement (8-10 hours), new fuel pumps and sender units, fuel filter, and often multiple injectors. V12 has 12 injectors at $200+ each. Tank replacement alone is $1,500 in parts.

Estimated cost: $3,000-6,500

Typical onset: 60,000-100,000 mi

Symptoms: Battery dies after 2-3 days of sitting, Voltage gauge showing undercharging (below 13V), Multiple electrical gremlins, Battery warning light intermittent, Alternator whining

Fix: The 150A alternator's voltage regulator fails, and the complex electronic architecture creates parasitic draws. Alternator replacement is 3-4 hours (cramped V12 bay). Must diagnose parasitic draw with ammeter—often SAM modules or trunk components staying awake. Battery is trunk-mounted, requires coding after replacement.

Estimated cost: $800-1,500