Question about an Oil leak

[Gasman]

Hi guys, I am just trying to find out whether the problem I have is a recognised one.

Today I found oil under the bike after a ride, after taking a closer look I see that the leak has been caused by one of the half round rubber blanking plugs (attached to the cam cover gasket) has become displaced from it's correct position. (It is the forward most LHS one).

My bike is a 2002 model and as far as I know the cam cover has not been removed previously.

Has anyone heard of this before? I was wondering whether it could possibly be related to any kind of breather blockage problem ( clutching at straws a bit )