Lot M2708: 1991 Mercedes-Benz 500SL

Great question! The 1991 Mercedes-Benz 500SL (chassis code R129) is a beloved roadster, but there are several well-documented issues you should know about:

🔴 Critical Issues

1. Biodegradable Wiring Harness (The Big One) This is the most infamous problem on early R129s. Mercedes used an environmentally-friendly wiring insulation in 1991-1995 that actually biodegrades over time. The coating cracks and flakes off, causing short circuits. This affects the engine harness, throttle actuator, and main wiring harness. A 1991 model is right in the affected range. Replacement costs can run $1,500-3,000+.

2. Hydraulic Soft-Top System The electro-hydraulic convertible roof has multiple failure points—cylinders leak (especially front cylinders), hydraulic pumps fail, and lines can crack. The rollover bar uses the same hydraulic fluid and can also fail to deploy. With this car having a removable hardtop, you’ll want to test the soft-top operation thoroughly before buying.

🟡 Common Maintenance Items

3. Distributor Cap Moisture Early R129s like the 500SL are notorious for damp distributor caps (there are two on this V8), causing misfires and rough running—especially in humid or wet conditions.

4. Instrument Cluster Electronics Gauges can flicker, warning lights may malfunction, and displays can fade. This is usually capacitor-related and repairable by specialists.

5. Oil Leaks The M119 V8 is generally robust but prone to valve cover gasket leaks and rear main seal leaks as it ages.

✅ The Good News About This Specific Car

This particular 500SL has just 56,130 miles—remarkably low for a 35-year-old car! The listing also notes recent work: new radiator, new fuel pump, and fresh oil change—all good signs of attentive care. Lower-mileage cars tend to have fewer of the age-related wiring issues, but the biodegradable harness degradation is time-based, not mileage-based.

My recommendation: Before moving forward, have a Mercedes specialist inspect the engine wiring harness condition and test the soft-top operation multiple times. These two items can be expensive gotchas!

Would you like me to help you find similar R129 SLs for comparison, or search for lower-priced alternatives?