Hi Rob,
you might want to check whether there have been any previous modifications to the timing cover. I suffered from a terrible oil leak from the cork gasket due to holes having been drilled though the dynamo chain area into the inner timing case area by a previous owner. For what purpose, I can only guess at, and assume it was to get more lubrication to the chain. I got the holes sealed up, and the iming cover, especially the cork washer area, are completely leak free.
See my previous posting - holes in timing cover.
John