1996 MERCEDES-BENZ S500 W140

Typical onset: 80,000-150,000 mi

Symptoms: rough idle or stalling, misfires under load, check engine light with multiple cylinder codes, fuel smell in engine bay, hard starting when hot

Fix: The engine harness insulation literally disintegrates into sticky goo from heat and age. Complete harness replacement requires 12-16 hours labor, involves removing intake manifold, fuel rails, and dozens of connectors. Some shops offer rebuild service instead of OEM replacement to save cost.

Estimated cost: $2,500-4,500

Typical onset: 120,000-180,000 mi

Symptoms: white smoke from exhaust, coolant loss with no visible leaks, milky oil on dipstick, overheating under load, rough running after long highway drives

Fix: M119 develops head gasket leaks between cylinders or into coolant passages, often from overheating episodes or deferred cooling system maintenance. Both heads off, resurface, new gaskets, timing chain components while you're in there. 25-35 hours labor. If you see machine shop bills or valve work needed, add $1,500-2,500. Many owners opt for upgraded MLS gaskets.

Estimated cost: $4,500-7,500

Typical onset: 100,000-160,000 mi

Symptoms: harsh 2-3 shift or flare on upshift, limp mode or stuck in second gear, delayed engagement from park, erratic shifting when cold, transmission fault codes

Fix: The 722.6 five-speed has an electrohydraulic valve body with a conductor plate that cracks solder joints or develops internal wear. Requires dropping pan, replacing valve body or conductor plate, new filter, fluid flush. 6-10 hours labor depending on whether full valve body or just plate. The transmission oil cooler lines also rot and leak, adding 2-3 hours if you're doing both jobs together.

Estimated cost: $1,800-3,200

Typical onset: 90,000-140,000 mi

Symptoms: rear end sags overnight or after sitting, uneven ride height side-to-side, hydraulic pump runs constantly, groaning noise from rear when turning, low hydraulic fluid warning

Fix: Rear hydraulic accumulators, struts, and distribution block seals fail. One or both rear struts typically leak first. Each strut is 3-4 hours labor, accumulators another 2-3 hours. Many owners convert to conventional coil springs with Arnott kits to escape the hydraulic nightmare, which is 4-6 hours labor but eliminates future hydraulic headaches.

Estimated cost: $1,200-2,800

Typical onset: 70,000-120,000 mi

Symptoms: HVAC blend doors stuck or blowing wrong temperature, cruise control intermittent or inoperative, central locking slow or non-functional, soft brake pedal with hissing, rough idle with high idle speed

Fix: Mercedes used biodegradable rubber vacuum lines throughout that crack and leak after 15-20 years. Requires methodically replacing every vacuum line under the hood and behind the dash. 8-12 hours labor if you do it right and replace everything at once. Vacuum pump and check valve often need replacement simultaneously.

Estimated cost: $800-1,600

Typical onset: 60,000-100,000 mi

Symptoms: clunking over bumps, wandering on highway, steering wheel off-center after hitting bumps, uneven tire wear on inside edges, vibration at 45-60 mph

Fix: Lower thrust arms and upper control arm bushings wear out, creating slop in the front end. Complete front suspension refresh with thrust arms, ball joints, tie rods, and bushings is 8-12 hours labor. Alignment required afterward. Most shops recommend doing everything at once since you're paying for the same labor access.

Estimated cost: $1,500-2,800

Symptoms: one or both headlights flicker then die, headlight works intermittently, headlight stays on dim/parking light mode, bulb appears blue but very dim output

Fix: Early xenon systems use separate ballasts and igniters that fail independently. Each side is 1-2 hours labor to diagnose and replace. OEM parts are discontinued, aftermarket quality varies wildly. Some owners retrofit HID kits or LED bulbs to escape the xenon parts chase.

Estimated cost: $600-1,200