1995 MERCEDES-BENZ 500SL R129

Symptoms: intermittent no-start conditions, random electrical gremlins, engine running rough or misfiring, check engine light with multiple unrelated codes, melting insulation with visible green oxidation on wires

Fix: Mercedes used soy-based insulation from 1992-1996 that literally disintegrates. Complete engine harness replacement is 12-16 hours labor. Many owners also replace the chassis harness at the same time to avoid doing the job twice. Aftermarket harnesses available but OE quality varies.

Estimated cost: $2,800-5,500

Typical onset: 80,000-150,000 mi

Symptoms: convertible top operates slowly or stops mid-cycle, hydraulic fluid pooling in trunk area, trunk won't open or close electrically, whining hydraulic pump when top operates, fluid visible on cylinders behind rear seats

Fix: The hydraulic cylinders develop seal leaks with age. Top cylinders are 4-6 hours, trunk cylinders add another 2-3 hours. Pump replacement if worn is another 3-4 hours. Must use Pentosin CHF 11S fluid. Many techs rebuild cylinders rather than replace to save cost.

Estimated cost: $1,200-3,200

Typical onset: 120,000-180,000 mi

Symptoms: white smoke from exhaust on cold start, coolant loss with no visible leaks, oil contamination in coolant reservoir, rough idle when warm, overheating under load

Fix: The M119.960/970 V8 is known for head gasket failures, often combined with cracked heads or warped surfaces if overheated. Both heads require 18-24 hours labor, includes timing chain tensioner and guide replacement while in there. Some engines need valve guide work simultaneously.

Estimated cost: $4,500-7,500

Typical onset: 100,000-160,000 mi

Symptoms: harsh or delayed shifts, no upshift past 2nd or 3rd gear, limp mode with transmission fault codes, slipping between gears, no movement in drive or reverse

Fix: The 722.5 transmission develops conductor plate failures and valve body wear. Conductor plate replacement is 4-6 hours including fluid and filter. If valve body needs work, add 2-3 hours. Must use correct Mobil ATF 3309 fluid or Mercedes-approved equivalent. Address sooner rather than later to prevent hard part damage.

Estimated cost: $1,500-2,800

Typical onset: 100,000+ mi

Symptoms: hard starting especially when hot, rough idle or stumbling, loss of power under acceleration, fuel smell from engine bay, fuel leaking from distributor, black smoke under hard throttle

Fix: The KE-Jetronic fuel system uses a mechanical distributor that wears internally. Rebuild or replacement is 6-8 hours, includes checking injector seals and fuel accumulator. Fuel pressure must be precisely adjusted. Many cars also need the fuel filter housing replaced due to rust perforation. This is the last year of KE-Jetronic before switching to electronic injection.

Estimated cost: $2,200-4,000

Typical onset: 80,000-140,000 mi

Symptoms: rear end sags especially with weight, SLS warning light illuminated, leaking shock absorbers, suspension pump runs continuously, uneven ride height side-to-side

Fix: The self-leveling rear shocks leak and accumulators fail. Both rear shocks plus accumulators is 4-6 hours labor. Can convert to conventional springs/shocks for $800-1,200 if you don't mind losing the auto-leveling feature, but affects ride quality. OE replacement maintains proper handling characteristics.

Estimated cost: $1,800-3,200

Symptoms: windows drop slowly or stick halfway, top won't operate unless windows manually positioned, window falls into door, one-touch up/down doesn't work, top mechanism errors out mid-cycle

Fix: Window regulators are weak and limit switches corrode. Each window regulator is 2-3 hours labor. Limit switches are 1-2 hours each but require top mechanism access. Windows must fully retract before top operates, so failed regulators prevent top operation. Stock up on door lock vacuum actuators while you're in there — they fail too.

Estimated cost: $600-1,200