2004 MERCEDES-BENZ SLK320 R170

Typical onset: 80,000-140,000 mi

Symptoms: Milky oil on dipstick or oil cap, Unexplained coolant loss with no external leaks, White smoke from exhaust on cold start, Overheating with clean cooling system, Coolant smell from oil filler

Fix: M112 blocks from this era suffer from micro-porosity allowing coolant into oil galleries. No head gasket leak—it's the block itself. Requires complete engine replacement or short block swap. 18-24 labor hours for R&R plus machining if salvageable core available. Most shops recommend used low-mileage engine swap due to parts availability.

Estimated cost: $4,500-8,000

Typical onset: 100,000-150,000 mi

Symptoms: Deep knocking from lower engine on cold start that may disappear when warm, Metallic rattling under acceleration, Low oil pressure warning intermittently or constantly, Metal shavings in oil during changes, Sudden catastrophic failure with no prior warning in some cases

Fix: The M112 has marginal oiling to mains and rods, especially with extended oil change intervals or low-quality oil. Bearing wear leads to knock and eventual spun bearing. Requires complete teardown, crank polishing or replacement, new bearings, plus address any scoring. 20-28 labor hours. Often totals the car given values.

Estimated cost: $5,000-9,500

Typical onset: 90,000-130,000 mi

Symptoms: Harsh 2-3 or 3-4 shifts, Limp mode with transmission fault codes, Slipping between gears under light throttle, No upshifts past 2nd or 3rd gear, Intermittent flaring during shifts

Fix: The 722.6 five-speed auto uses a conductor plate (wiring harness inside the valve body) that cracks from heat cycling. Solenoids also fail. Requires valve body removal, new conductor plate, 13-pin connector, solenoids as needed, fresh fluid and filter. 6-9 labor hours. Sometimes requires full transmission rebuild if internal damage occurred.

Estimated cost: $1,800-3,500

Typical onset: 70,000-110,000 mi

Symptoms: Red transmission fluid pooling under engine bay center, Transmission overheating warnings, Burnt transmission fluid smell, Low fluid level on dipstick, Lines visibly wet or corroded at radiator connections

Fix: Steel cooler lines rust through at the radiator, and the cooler itself can crack internally. External leaks are obvious; internal cooler failures mix coolant and ATF (destroys transmission). Replace lines, external cooler, and flush system. 3-5 labor hours for lines, more if radiator or transmission contaminated.

Estimated cost: $800-2,200

Symptoms: Top operates slowly or stops mid-cycle, Hydraulic fluid leaking in trunk near pump or cylinders, Top won't latch or unlatch electrically, Groaning or laboring sounds during top operation, Top control illuminated or flashing warning light

Fix: The vario-roof system uses hydraulic pump and cylinders that leak from aged seals or develop internal wear. Requires pump rebuild or replacement and cylinder seal kits. Top must be manually positioned and system bled after repair. 4-7 labor hours depending on which components fail. Fluid mess in trunk is diagnostic.

Estimated cost: $1,200-2,800

Typical onset: 80,000-140,000 mi

Symptoms: No-start condition with cranking but no firing, Intermittent stalling when hot, Long crank time before starting, Check engine light with P0335 or P0340 codes, Engine dies while driving and restarts after cooling

Fix: Hall-effect sensors fail from heat exposure on the M112. Crank sensor is behind the starter (remove starter for access), cam sensors at cylinder head front. Diagnosis requires scanner to confirm codes. 1.5-3 labor hours depending on which sensor and access. Parts are cheap; labor varies by location.

Estimated cost: $300-700

Typical onset: 60,000-100,000 mi

Symptoms: Clunking over bumps from front end, Steering wander or vague on-center feel, Uneven inside tire wear, Visible cracking or tearing of rubber bushings, Excessive play in ball joints during inspection

Fix: R170 front lower control arms use pressed bushings that wear and crack. Ball joints also fail. Mercedes typically replaces entire arms versus pressing bushings (faster, guaranteed fitment). Need alignment after. 3-4 labor hours for both sides plus alignment.

Estimated cost: $900-1,600