I agree that the diagnosis sounds wrong.

Having said that, if you have the original timing chain, tensioner, and guide rails in your '89 420 SEL, I don't think you'll find a person on this site that wouldn't recommend replacing them.

Do a search on 'timing chain' and you can read these threads all day and night.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".