There is an old saying that you need to get the oil hot each time you run the engine. This is to drive out the moisture that may be in the engine case. Well if you ever doubted that it might be true, check out the goo on this rocker cover (yep, mayonnaise = water and oil, hold the egg white)

Also note that the cork gasket was just starting to fail (on the right – bottom of the cover). Cork gaskets are good for about 200 hours of engine operation max. The cork cooks slowly and looses it spring and allow hardware to fall out and to let leak start. Red Silicone gaskets are the way to go and they are reusable (SLR75906 – part number).