IMS and RMS are two entirely different issues and they should not be discussed in the same context.
IMS = Intermediate Shaft
RMS = Rear Main Seal
The RMS issue is a leaking seal, nothing more. It's actually quite rare to find a car with a leaking RMS these days - most leaking seals have been replaced with the latest version which doesn't leak. Those motors which could not be fixed because they were out of spec were replaced by Porsche under warranty. RMS issues are easy to spot and the issue is harmless, except maybe a spot of oil on the garage floor.
The IMS though is a different story. (OK - IMS seal leaks can occur, but like the RMS these are harmless and easy to fix.)
IMS *bearing* failures are a real problem. The bearing that supports the intermediate shaft was poorly designed and prone to failure. It gives little to no warning before it fails and when it does fail it destroys your motor. Dead, done - you're not rebuilding the old motor because it's fu^%ed. You're buying a new motor.
This has been discussed to death on line, and then discussed a zillion times more. In the end though, the answer is always the same, only Porsche knows, and they probably don't even know, and at any rate they are *not* saying anything.
Problem is that Porsche replaced a lot of engines in the first five years or so, all under warranty. Not all of them were IMS issues, some were RMS issues that could not be solved, some were for cracked heads, some were for porous castings, some were just service manager's taking the easy route to making a customer happy. Porsche took all of the motors back for analysis. most were re-manufactured with upgrades and these went back into the system.
These days we rely on the experience of knowledgeable independent repair people, but they only see cars with problems so they have a biased view.
After all the chatter is done, a figure of between 1% and 5% seems to be consensus, with the later 3.6 litre cars suffering less than the early 3.4 litre cars, and with early Boxsters being the worst....depending on who you talk to because of course there were a lot more Boxsters sold, so in absolute terms there will also be more failures.
Now don't ask again because M96 owners get annoyed by the question.
