1991 MERCEDES-BENZ SL

Typical onset: 60,000-120,000 mi

Symptoms: Random misfires and rough idle, Check engine light with multiple cylinder codes, No-start conditions, Electrical gremlins throughout the car, Visible cracking and exposed copper on engine harness

Fix: Mercedes used soy-based insulation that disintegrates. Engine harness replacement is 12-16 hours labor. Must also inspect cabin and chassis harnesses. Many shops subcontract harness rebuilds to specialists.

Estimated cost: $2,500-4,500

Typical onset: 80,000-150,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Overheating, Milky oil on dipstick or oil cap, Rough idle and loss of power

Fix: The M119 V8 is prone to head gasket failure between cylinders or into coolant passages. Requires heads-off job, 20-28 hours labor. CRITICAL: must also replace head bolts (they stretch), check head flatness, and address any wiring harness issues simultaneously or you'll do it twice. Often find cracked pistons or worn rings once you're in there.

Estimated cost: $4,500-7,500

Symptoms: Top operates slowly or stops mid-cycle, Hydraulic fluid leaking in trunk, Top won't latch or unlatch, Pump runs continuously, One side of top moves while other doesn't

Fix: Hydraulic cylinders, lines, and pump all fail with age. Diagnosis is 1-2 hours. Cylinder replacement is 4-6 hours per side, pump is 3-4 hours. Seals dry out regardless of mileage. Full system overhaul recommended if one component fails.

Estimated cost: $1,800-3,500

Typical onset: 100,000+ mi

Symptoms: Transmission fluid spraying onto exhaust or undercarriage, Sudden loss of all gears, Burning smell, Transmission slipping after long highway drives, Visible fluid trail under car

Fix: Steel cooler lines rust through where they pass near exhaust. Catastrophic failure dumps all ATF in seconds, destroying transmission if driven. Replacement is 3-5 hours depending on rust. ALWAYS inspect these lines during any under-car service on high-mileage examples.

Estimated cost: $600-1,200

Typical onset: 80,000-150,000 mi

Symptoms: Rear end sagging when parked, SLS warning light, Compressor runs constantly, Uneven ride height side-to-side, Clunking over bumps

Fix: Hydraulic accumulators and valve blocks fail. Struts leak. Compressor wears out from compensating for leaks. Complete system replacement (both struts, accumulators, compressor) is 8-12 hours. Many owners convert to conventional springs/shocks (Arnott kit) for $1,500-2,000 parts + 4-6 hours labor.

Estimated cost: $2,500-4,000

Symptoms: Door locks cycling randomly or not locking, HVAC blend doors not responding, Hissing sound from dash, Trunk and gas cap won't unlock, Climate control stuck on one setting

Fix: Hard vacuum lines and rubber connectors become brittle. Vacuum pump diaphragm fails. Diagnosis requires smoke test or pressure decay test, 2-3 hours. Line replacement throughout car is 6-10 hours. Pump replacement is 2 hours.

Estimated cost: $800-2,000