Wolfgang:

Get you chain tensioner checked! Knocking/ringing at 35-45 mph is often a result of a leaking chain tensioner allowing the chain to slap. This can break plastic chain guides and cause the chain to jump in some motors, causing all sorts of expensive damage.

This is a major pain in a 115 chassis, not too bad in a 123 (the AC compressor in a 123 isn't in the way).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!