Hi benz-vettes

it's not so much the chain as the tensioners that need to be replaced at certain intervals/years. The chain is checked for stretch at the time the tensioners are replaced and based on the stretch a decission is made on the chain.
Do a search, there is plenty in the archives.

Based on age, I would have both cars checked out. I got new tensioners on my 87 420 with then about 45,000 miles on it and the mechanic reported some of them already partly broken.
I believe stevebfl has given a recommendation when to replace the tensioners based on miles and age.

Good luck

Reinhard Kreutzer