Buying a used Porsche 911 (996/997) or Boxster/Cayman (M96/M97): what to check

A used-car buyer's guide to M96/M97 Porsches (996, 997.1, 986 and 987 Boxster and Cayman): IMS bearing, bore scoring, rear main seal, AOS, water pump and clutch, with real owner-reported prices.

Covers: 911 Carrera (996 and 997.1), Boxster (986 and 987.1) and Cayman (987.1) with the M96 or M97 flat six. Not the Turbo, GT2 or GT3, which use a different engine.

These are some of the best-value Porsches out there, and they come with a reputation. The IMS bearing gets the headlines, but bore scoring, the air-oil separator, water pumps and rear main seal leaks are what most owners actually deal with. A good pre-purchase inspection on one of these is not optional. It's the single best money you'll spend.

What to look for

IMS bearing history. Has it been replaced or upgraded, and by whom? Get the invoice.
Smoke on startup or a big puff after idling, which can be the air-oil separator.
Oil drips between the engine and transmission (rear main seal).
Coolant leaks at the water pump or cracks in the expansion tank.
Ticking or knocking, and oil consumption, which can point to bore scoring.
Clutch: high engagement or slip, and when it was last done.
Over-revs on the DME report, which show whether the engine has been revved past redline, often from a missed shift.

Problems by mileage

Roughly when owners and shops report each problem. Plenty of cars go longer and some fail sooner, so use this to know what to ask about, not as a schedule.

Rear main seal (RMS) leak Usually about 30k–120k miles · Routine wear
Oil drip between the engine and transmission.

IMS bearing Usually about 40k–120k miles · Can wreck the engine or gearbox
Metal flakes in the oil filter, rattle from the back of the engine. Often no warning.

Water pump Usually about 50k–80k miles · Fix it when it starts
Coolant drip under the middle of the car, coolant smell, temps creeping up.

Air-oil separator (AOS) Usually about 50k–100k miles · Fix it when it starts
Big puff of smoke at startup, high oil use, rough idle, oil in the intake.

Coolant expansion tank cracks Usually about 60k–140k miles · Routine wear
Coolant smell in the trunk area, low coolant warning.

Bore scoring Usually about 60k–150k miles · Can wreck the engine or gearbox
Ticking, oil consumption, sooty tailpipe on one side.

Full Porsche M96/M97 problem list with what each fix costs →

Repair costs to budget for

Only jobs we have cited owner reports for. If a job isn't here, we don't have enough real prices for it yet.

Medians of what owners reported paying in public forum posts, with ranges counted at their midpoint. They aren't quotes, they come from different years and cities, and they aren't adjusted for inflation. Click any job to see every report and its source.

Job	Non-dealer median reports	Dealer median reports	Total reports
Porsche 986/996 IMS bearing	$4,000 5	n/a 0	5
Porsche 996/986 air-oil separator (AOS) replacement	$1,200 5	$1,225 2	7
Porsche Boxster/Cayman/911 (M96/M97) water pump Small sample	$950 1	n/a 0	1
Porsche 911 (996/997) clutch replacement	$2,625 4	$3,500 3	7

Pre-purchase inspection checklist

Ask the shop doing the inspection to cover these, on top of their normal checks.

Pull the DME report for over-rev counts and hours.
Borescope the cylinders for scoring. Not every shop has one, so ask.
Check the oil filter for metal (IMS and bearing debris).
Inspect the rear main seal area and the AOS.
Check coolant hoses, the expansion tank and water pump.
Look at the clutch and dual-mass flywheel history.
Check for a documented IMS upgrade and which kit was used.