Well, i have also done loads or reading and re-reading as well. I have been to see a couple of Porsche specialists on the very matter and the last guy i spoke to i found very knowledgeable and basically the conversation lead to the overall design of the Boxster engine. My 986 is a 2004 2.7 car and has the 3 timing chains which i am told are an improvement from the previous 5 timing chains on, i think, the 2.5 cars. Anyways the IMS was intended to last the lifetime of the engine, which as we all know can and probably will fail prematurely. I was looking to upgrade my IMS, RMS and clutch all together mostly for peace of mind, but most of the specialist ive spoken to tell me even the upgraded bearings can still fail. i am told the oil fed bearings so far are the best option. As it is not intended to be replaced they recommend having the engine removed strip down and rebuilt with complete new IMS shaft and full seal kit. But that is about £4500.00 and then the bearing can still fail. Apparently to save money porsche made both cylinder heads the same , rather than on left hand and one right hand, thus the need for an intermediate shaft to drive the timing chain at each end of the engine.
my car has done 86k miles, 40k done by me in the last 5 years. I probably won't get an upgrade at the moment. its due for a service end of this month so i will have the oil thoroughly checked for debris then plan it from there.
i found some good info on the
Porsche servicing, repairs, engine rebuilds, reconditioned wishbones and cars for sale - near Bolton, North West England. website and thats who the specialists i have spoken to have recommended for the engine rebuild. i know they are here in the UK but you may well find some useful info.
from what i can tell and read it is completely pot luck if and when it will fail. I try not to worry about it, but i still do.
sorry if i dragged on a bit but that is the info i have read and been told.
hope it helps
steve.