2002 MERCEDES-BENZ SLK320 R170

Typical onset: 70,000-120,000 mi

Symptoms: Sudden rattling or knocking from deep in the engine bay, especially on cold start, Metal shavings in oil, glitter on magnetic drain plug, Check engine light with misfire codes or low oil pressure warning, Catastrophic failure: seized engine, no restart

Fix: The M112 balance shaft gears are plastic-toothed and strip without warning, dumping debris into the oil system and wiping bearings. Requires full short block replacement or complete engine rebuild with new balance shaft assembly, main bearings, rod bearings, often pistons and rings. 25-35 hours labor for R&R and rebuild, plus machine work if heads need resurfacing.

Estimated cost: $5,000-9,000

Typical onset: 80,000-130,000 mi

Symptoms: Transmission fluid spots under car, usually front-center, Pink or red fluid leaking near radiator area, Low transmission fluid level, harsh or delayed shifts, Burnt transmission smell if run low for extended period

Fix: The hard lines and rubber hoses running to the transmission cooler corrode and crack. Replace cooler lines, top off fluid, may need transmission service if run low. 2-3 hours labor, straightforward if caught early before transmission damage.

Estimated cost: $400-700

Typical onset: 60,000-100,000 mi

Symptoms: Clunking when shifting from Park to Drive or Reverse, Vibration at idle that smooths out at higher RPM, Visible sag or torn rubber on transmission mount inspection, Driveline shudder during acceleration

Fix: The 722.6 five-speed auto sits on rubber mounts that deteriorate. Replace transmission mount, often engine mounts at same time since they fail similarly. 2-3 hours labor for trans mount alone, 4-5 if doing engine mounts together.

Estimated cost: $350-600

Typical onset: 90,000-140,000 mi

Symptoms: Oil weeping from head/block mating surface, visible crusty buildup, Slight coolant loss over time, no obvious external leaks, Faint coolant smell after hot shutdown, Not the catastrophic blown gasket—more of a slow seep

Fix: M112 heads can seep at the gasket over time, though full combustion-to-coolant failure is less common than balance shaft issues. If catching early seepage, some owners defer; if doing heads off for any reason, replace gaskets, resurface heads, new bolts. 12-16 hours labor.

Estimated cost: $2,200-3,500

Typical onset: 80,000-120,000 mi

Symptoms: Rough idle, stumbling on acceleration, Intermittent stalling, especially when fuel tank below 1/4, Check engine light with fuel trim or misfire codes, Hard starting after sitting overnight

Fix: Inline fuel filter clogs with age; in-tank pump can wear. Filter change is 1 hour, pump replacement 3-4 hours (tank drop). Always replace filter first before condemning pump.

Estimated cost: $200-350 filter, $800-1,200 pump

Typical onset: 60,000-100,000 mi

Symptoms: Top operates slowly or won't latch fully, Hydraulic fluid dripping near trunk hinges or under rear seats, Top stuck halfway, error message in instrument cluster, Visible oil on top mechanism or staining in trunk

Fix: The hydraulic cylinders and hoses for the folding hardtop age and leak. Requires new cylinders, seals, sometimes fluid reservoir or pump. 4-6 hours labor, must bleed system afterward. Not a breakdown issue but kills resale value.

Estimated cost: $1,200-2,000