1996 MERCEDES-BENZ S600

Typical onset: 80,000-150,000 mi

Symptoms: Coolant mixing with oil (milky dipstick), External coolant leaks from head gasket area, Overheating, Rough running or misfires, White exhaust smoke

Fix: The M120 aluminum block uses threaded inserts for head bolts that pull out under torque cycling, causing head gasket failure. Proper fix requires TimeSerting all 24 head bolt holes per bank (48 total), new head gaskets, machining, and often valve work. Expect 40-60 labor hours for both banks plus machine shop time. Shortcuts fail quickly.

Estimated cost: $12,000-18,000

Typical onset: All mileages (age-related, 25+ years)

Symptoms: Intermittent no-starts, Random warning lights, Gauges acting erratically, Windows/seats not working, Check Engine light with multiple random codes, Visible crumbling insulation in engine bay

Fix: Mercedes used soy-based insulation that biodegrades completely. Engine harness is worst (behind engine on firewall), but cabin harness also fails. Requires complete harness replacement, not patch repairs. Engine harness alone is 20-30 hours; full car can exceed 60 hours. Genuine parts discontinued; aftermarket or used only options.

Estimated cost: $4,500-8,000

Typical onset: 100,000-180,000 mi

Symptoms: Harsh 2-3 or 3-4 shifts, Transmission slipping, Delayed engagement into gear, Limp mode (stuck in 2nd gear), No upshifts past 3rd

Fix: The 722.633 5-speed transmission's valve body solenoids and conductor plate (circuit board) fail from heat and fluid contamination. Requires trans pan removal, valve body R&R, and new conductor plate. Often combined with fluid/filter service. 8-12 hours labor. Use only genuine MB fluid (Fuchs Titan ATF 3353).

Estimated cost: $2,200-3,500

Typical onset: 60,000-120,000 mi

Symptoms: Clunking when shifting D to R, Excessive vibration at idle, Visible engine movement when revving, Transmission tunnel heat, Steering wheel vibration

Fix: The V12's weight and vibration destroy hydraulic mounts prematurely. All four engine mounts plus transmission mount should be done together. Requires engine support and special tooling. 10-14 hours for complete job. Aftermarket mounts fail quickly; use OE or OEM equivalents only.

Estimated cost: $2,800-4,200

Typical onset: 80,000-140,000 mi

Symptoms: Hard starting when warm, Loss of power at highway speeds, Stumbling under acceleration, Fuel smell in cabin or trunk, Check Engine light with lean codes

Fix: Twin in-tank fuel pumps fail (one per bank), and the fuel filter clogs if not changed every 30k mi. Plastic fuel lines under car also crack. Tank drop required for pump access (6-8 hours each pump). Filter is 1 hour. Fuel line replacement adds 4-6 hours depending on extent.

Estimated cost: $1,200-2,800

Typical onset: 90,000-150,000 mi

Symptoms: Car sitting low (especially rear), ABC warning light, Rough ride, Pulsation pump running constantly, Fluid leaks at struts or lines

Fix: Active Body Control struts leak internally, and high-pressure lines crack. Struts are $1,200-1,500 each; pulsation pump is $2,500+. ABC fluid is special and expensive. One failed strut requires replacing both on same axle. Diagnosis requires Star diagnostic tool. Labor: 4-6 hours per strut, 8-10 for pump.

Estimated cost: $3,000-8,000

Typical onset: 70,000-130,000 mi

Symptoms: Intermittent no-start (cranks but won't fire), Stalling while driving, Oil puddles under car, Oil on bellhousing, Burning oil smell

Fix: Crank sensor fails from heat; it's buried behind the engine requiring transmission removal to access properly (some techs go from above with extreme patience). Rear main seal and oil pan gaskets also leak commonly. Sensor alone if accessed from above: 6-8 hours. With transmission drop for rear main: 18-24 hours.

Estimated cost: $800-4,500