Red rubber gasket for later side (tappet) covers on the back of the block under the exhaust manifold.
The late covers have a U section where the gasket sits and the gasket is around 6mm thick.
Hint: stretch the new rubber larger as they are all a little small for the plate... and a small amount of silicone around the head of the retaining bolt stops another oil leak.
Sold per each.
We can usually supply used later model side plates for your early engine.