Oil leak?

I saw that the back of the oil filter was covered with some oil and around it on the sump a bit too. Only in the neighbourhood of the oil filter. Known problem?

no, check the filter seal is seated correctly, not old and perished or has dirt on it. Also check the filter seating on the underisde of the sump which the seal sits up against for any roughness.... may makes a leak path, also check the filter is tight..... duh....

So You don't think of the O-ring of the engine?