That dark spot on the front corner? That's a low point, so oil could be seeping from anywhere. Replace the valve cover gasket, just in case. No need for any goo on the gasket other than a smear of grease. While you are there, remove the breather & check the state of the tube under the clamp - it does go brittle & cracks (& later breaks). If this is so, there is likely to be oil collecting in the channel in the cylinder straight underneath the breather.
Mal.