The 2004 Boxster S (986.2 generation) with the M96 3.2L flat-six is a driver's car with one elephant in the room: intermediate shaft bearing failure and related bottom-end issues that can grenade an otherwise solid engine. When maintained properly and if the IMS bearing has been addressed, they're rewarding mid-engine sports cars, but you're buying into potential catastrophic engine expense.
Intermediate Shaft (IMS) Bearing Failure
Occasional · high severityTypical onset: 40,000-80,000 mi
Symptoms: metallic rattling or grinding from engine bay at idle, metal shavings in oil or magnetic drain plug, catastrophic engine failure with no warning, Check Engine Light with cam/crank correlation codes in some cases
Fix: Proactive IMS bearing replacement requires engine-out or rear main seal access, 12-16 hours labor. If it fails and takes out the engine, you're looking at complete engine rebuild or replacement with machine work on crank and cylinders. Many owners do preventive replacement between 40k-60k miles.
Estimated cost: $2,500-4,000 for proactive IMS upgrade; $12,000-18,000 for full engine rebuild after failure
Bore Scoring / Cylinder Wall Damage
Occasional · high severityTypical onset: 60,000-100,000 mi
Symptoms: blue smoke on cold start that clears after warmup, excessive oil consumption (more than 1 qt per 1,000 mi), loss of compression in one or more cylinders, rough idle and misfires
Fix: M96 engines are prone to localized cylinder scoring due to design issues with cooling and oil delivery. Requires complete disassembly, bore/sleeve or replacement cylinders, new pistons and rings. 35-45 hours labor for full rebuild.
Estimated cost: $10,000-16,000
Rear Main Seal (RMS) Oil Leak
Common · medium severityTypical onset: 50,000-90,000 mi
Symptoms: oil spots under car after sitting overnight, oil visible on underside of transmission bell housing, oil dripping from engine/trans junction, burning oil smell from heat
Fix: Dual-row RMS design on M96 is notorious for leaking. Requires transmission removal for access, good time to do IMS bearing and clutch if not already done. 10-14 hours labor for seal alone, but smart to bundle jobs.
Estimated cost: $1,800-2,800 for RMS alone; $4,500-6,500 if combining with IMS bearing and clutch
Coolant Expansion Tank and Hose Failure
Common · medium severityTypical onset: 60,000-120,000 mi
Symptoms: coolant smell in cabin or engine bay, coolant puddles under car, overheating or high temp gauge readings, visible cracks in plastic expansion tank
Fix: Plastic tanks and aging rubber hoses become brittle. Tank itself is 2-3 hours; full cooling system refresh (all hoses, tank, thermostat) is 6-8 hours and recommended at this age.
Estimated cost: $600-1,000 for tank alone; $1,500-2,200 for complete system refresh
Convertible Top Hydraulic System Leaks
Common · low severityTypical onset: 70,000-110,000 mi
Symptoms: top operates slowly or stops mid-cycle, hydraulic fluid visible in trunk area or on lines, whining pump noise during top operation, top fails to latch or unlatch properly
Fix: Hydraulic lines, cylinder seals, and pump can leak. Diagnosis 1-2 hours, line replacement 3-5 hours depending on location, pump replacement 4-6 hours. System must be bled after repair.
Estimated cost: $800-1,800 depending on component
Mass Air Flow (MAF) Sensor Failure
Occasional · low severityTypical onset: 80,000-140,000 mi
Symptoms: rough idle or stalling, hesitation on acceleration, Check Engine Light with lean/rich codes, reduced power and poor fuel economy
Fix: Direct replacement, 0.5-1 hour labor. Cleaning can extend life temporarily but usually needs replacement.
Estimated cost: $400-650
Transmission and Engine Mount Deterioration
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: clunking when shifting or engaging clutch, excessive engine movement visible under acceleration, vibration through chassis at idle, drivetrain noise over bumps
Fix: Rubber mounts harden and crack. Both engine mounts and transmission mount typically need replacement. 4-6 hours labor for all mounts, transmission often requires dropping or supporting.
Estimated cost: $1,200-1,800
Buy only if IMS bearing has been done or you have $15k set aside for engine work—it's when, not if, on unaddressed examples, but post-IMS cars are fantastic drivers for the money.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.