2000 MERCEDES-BENZ 500SL R129

Typical onset: any mileage (age-related, 20+ years)

Symptoms: intermittent no-starts, random misfires, check engine lights that come and go, failed emissions tests, rough idle that moves cylinder to cylinder

Fix: Mercedes used soy-based insulation that crumbles into dust. Engine harness replacement requires 12-16 hours of labor—every connector, every sensor wire. Underhood harness is the critical one; some shops do chassis harness too if budget allows.

Estimated cost: $2,800-4,500

Typical onset: 120,000-180,000 mi

Symptoms: blue smoke on startup, quart of oil every 800-1,200 miles, carbon buildup on spark plugs, loss of power under load

Fix: M119 piston rings wear and oil control suffers. A proper fix is engine-out rebuild with new rings, hone cylinders, valve seals—40-50 hours labor. Many owners top off oil and drive it; rebuild cost often exceeds vehicle value at this age.

Estimated cost: $8,000-12,000

Typical onset: 100,000-150,000 mi

Symptoms: harsh 2-3 shift or flare, limp mode with trans fault codes, delayed engagement into gear, no upshift past second gear

Fix: 722.6 five-speed valve body develops worn bores and the 13-pin connector corrodes. Repair involves pan drop, valve body removal, rebuild or replacement, new conductor plate, fluid and filter—8-10 hours labor. Some techs replace the whole valve body assembly to save diagnostic time.

Estimated cost: $1,800-3,200

Typical onset: any mileage (age-related)

Symptoms: roof takes 30+ seconds to cycle instead of 15, hydraulic fluid pooling in trunk, roof stops mid-cycle and won't latch, whining pump noise

Fix: Aged seals in cylinders and lines leak. Full system overhaul means new cylinders, pump reseal, all lines and micro-filter—12-15 hours labor. Many owners live with slow operation and top off fluid quarterly rather than fix comprehensively.

Estimated cost: $3,000-5,000

Typical onset: any mileage (regional, salt exposure)

Symptoms: clunking over bumps from rear, steering wander or rear-end crabbing, visible rust perforation on subframe rails, failed state inspection in rust-belt states

Fix: Subframe mounts tear and subframe itself can rust through on northern cars. Subframe removal and replacement is 18-22 hours—exhaust, diff, suspension all come out. Replacement subframes from southern donors are common repair strategy.

Estimated cost: $3,500-6,000

Typical onset: 80,000-140,000 mi

Symptoms: no-start when hot, starts fine cold, stalling at idle after highway run, intermittent crank-no-start, P0340 or P0335 codes

Fix: Heat kills these sensors. Crank sensor is 2.5 hours (behind harmonic balancer), cam sensor 1.5 hours. Replace both at same time if one fails—they're age-related and second failure usually follows within months.

Estimated cost: $600-1,000

Typical onset: 90,000-130,000 mi

Symptoms: ABC warning light with car sagging, harsh ride, no damping, leaking struts with oily residue, pump whine on startup

Fix: Active Body Control struts leak, pump fails, or accumulator sphere ruptures. Single strut replacement is 3-4 hours, but all four usually need refresh at same interval. Pump rebuild 6-8 hours. This system is a financial sinkhole—many owners convert to coilover delete kits.

Estimated cost: $4,500-9,000