Tappet chest leak.

[Rick F]

I use them on all three of my Sevens - two fitted with "RP" type engines and one with a 1929 coil engine. On the latter I use a later style cover with new fixing holes drilled and the old one filled in - I have never been able to get those flat cork gasket to seal properly.

I tack the silicone gasket in place with the tiniest dob of superglue at each corner, which just stops the gasket falling out while fitting.

I have found them to be oil-tight and would definitely recommend them. I also use silicone gaskets between the block and crank-case, but have yet to try one on the sump.