M104 engine, right?

Watch for oil leaks from the oil filler cap, the gasket gets hard and will leak at speed, runs off the front of the engine.

Valve cover gasket will leak sometimes, too -- usually all over everywhere, though.

Don't know if the upper timing chain cover leaks on this engine like it does on the M103, but that's the right place.

None of the bolts for the tensioner go into the chain case as far as I know, so the work you did shouldn't have had any effect on the leak unless you took the valve cover off and didn't replace the gasket.

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!