2009 MERCEDES-BENZ CLK550 C209

Typical onset: 60,000-120,000 mi

Symptoms: Rattling or marbles-in-a-can noise at cold start that may disappear when warm, Metallic grinding from front of engine, Sudden loss of oil pressure and engine seizure in worst cases, Check engine light with camshaft position sensor codes as collateral damage

Fix: The plastic balance shaft gears strip and send debris through the entire engine, wiping bearings and scoring cylinders. Requires complete engine teardown or replacement. If caught early with noise only, balance shaft delete kit plus front cover work runs 18-25 hours labor. If it grenades the motor, you're looking at reman long block or used engine swap at 30-40 hours labor plus the engine itself.

Estimated cost: $8,000-15,000

Typical onset: 80,000-130,000 mi

Symptoms: Red ATF puddles under front of vehicle, Transmission temperature warnings on dash, ATF level drops requiring frequent top-ups, Fluid visible on radiator end tanks or frame rail

Fix: The quick-disconnect fittings and hardlines at the radiator-mounted cooler corrode and leak. Usually requires cooler line replacement and often the auxiliary cooler itself. Radiator may need replacement if cooler is integrated. 3-5 hours labor depending on whether radiator comes out.

Estimated cost: $800-1,800

Typical onset: 70,000-110,000 mi

Symptoms: Clunk when shifting from Park to Drive or Reverse, Vibration at idle that changes when shifting to Drive, Excessive driveline movement visible when accelerating/decelerating, Transmission housing may contact subframe in extreme cases

Fix: The hydraulic transmission mount fails and the rubber degrades. Requires trans support and mount replacement. Often done with engine mounts since access is similar. 2-3 hours labor for trans mount alone, 5-6 hours if doing all mounts.

Estimated cost: $400-700

Typical onset: 90,000-140,000 mi

Symptoms: Check engine light with P0015/P0025 camshaft position timing codes, Rough idle or stumble on cold start, Reduced power and fuel economy, Rattling from valve covers during start-up

Fix: The variable valve timing solenoids and adjusters clog or fail, often from neglected oil changes. Requires valve cover removal, solenoid and sometimes adjuster replacement, plus thorough oil system flush. 4-6 hours labor per bank if doing adjusters, less if just solenoids.

Estimated cost: $1,200-2,500

Typical onset: 100,000-150,000 mi

Symptoms: Extended cranking before start, especially when hot, Hesitation or stumble under acceleration, Limp mode or stalling at highway speeds, Fuel pressure codes or low pressure on scan tool

Fix: The in-tank fuel pump fails or the lifetime fuel filter clogs despite Mercedes claiming it's non-serviceable. Pump replacement requires tank drop. Filter is integrated into pump assembly on many examples. 3-4 hours labor for pump, add 1 hour if also addressing filter housing rust/corrosion issues common in salt states.

Estimated cost: $900-1,500

Typical onset: 80,000-120,000 mi

Symptoms: Vehicle sits low in one corner or entire front/rear, Compressor runs constantly, Airmatic warning light and suspension warning messages, Bouncy or harsh ride quality

Fix: Air struts develop leaks at the rubber bellows or internal seals. Compressor wears out from overwork. Strut replacement is straightforward at 2-3 hours each corner. Compressor is another 2-3 hours. Many owners convert to conventional coil springs to eliminate future air suspension costs, which runs 6-8 hours labor.

Estimated cost: $1,500-3,500