My 87 had 130k on it when the chain broke and bent the valves on the drivers' side of the engine. I'm guessing the guide broke off and caused it, but I'm not sure - it happened at about 35mph, not at idle (which is probably more common).
I agree about the recall, but it's my impression that Mercedes doesn't care about cars they produced more than 5 years ago.
I'm wondering why your mechanic didn't change the rails when he did the job, they seem to be pretty inexpensive. What's the going rate on this repair?
The 560 engines don't seem to have this problem. The chain is different, it must make a difference.
2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino