I have 2 Sapph Cosworths, 1 is shell now, more or less forgotten about and the other hasnt turned a wheel since July. My M5 is the best thing I have bought and I love it. It had 128k on it with 3 previous owners, one of which was a BMW director, and full BMWSH from the same dealership from day 1. It had just had a service, new discs and pads all round and new Conti Sport rear tyres 12 miles before I bought it. I have the BMW reciept for it, it wasnt cheap either

I was talking to a friend of mine who is a senior tech for the local main dealers and he told me that pre facelift E39 M5's didnt have a one way valve in the VANOS oil feeds and it was not uncommon when they were a couple of years old for them to rattle for 20 seconds or so. Some have even been known to rattle up to 40 seconds on cold start . The revised models have the valve fitted so if they rattle for longer than 3-5 seconds it suggests VANOS problems. Mine is pre facelift and rattles for 3 seconds occasionally on cold startup.

I was talking to him because I suspected my timing chain tensioner was a tad noisy. Again he listened to it and said its normal for these motors to have a very very light chatter on idle. He then went into detail about the technical journals BMW sent out about these engines and their "quirks" like these.

His words were "keep it serviced and run it on good oil and they are bombproof, the only other thing they do is MAF's"