Probably just one of the rocker cover bolts, they're known to weep every now and again, best thing to do is whip the inlet manifold off, clean all the oil off the rocker cover, refit the manifold, drive it for a few days and see if there's any fresh oil seeping out, if there's a bolt leaking unscrew it and put some gasket sealant under the head of the bolt, that will sort the problem.
One of mine was leaking and the sealant fix worked and it's never leaked again.