There are two tricks for getting the cover gasket to seat:

1). you must clean both the valve cover edge and the seating surface on the head with solvent. Carb cleaner, laquer thinner, paint thinner, gasoline, whatever. Must be absolutely clean and dry. No oil, no sealant, nothing. I'd not buff with steel wool, either, for fear of making the surface rougher than the gasket will seal.

2). Installation: place clean dry gasket on valve cover. No sealant, no oil (especially no oil), no dirt in gasket, must be clean and dry. Clean the groove on the gasket if necessary to remove ALL grit, oil, or dirt. Fit cover to head, making sure the gasket stays on and isn't twisted anywhere. Lift cover an inch or so and thump square on the head firmly. Repeat lifting and thumping until the muffled "thumph" becomes a sharp, distinct "clop". This seats the gasket properly on the cover.

3). Tighten until the "feet" touch the head. No need to really reef down on the bolts, 15-25 Nm is quite sufficient. Use only the head of the ratchet, not the end of the handle, to tighten and you will be just about right.

This applies to all MB valve cover gaskets. Installed this way they don't leak.

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!