blackmercedes gives good advice, but to add my $0.02, generally speaking M119 engines don't seem to suffer the same chain wear that M117 / M116's do. Maybe it's because the chain tensioner in 119's does a better job. In any event, you might look at replacing the plastic rail guides and tensioner rail first.

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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".