Oil leak - sometimes

Ok so the Fasty is Rego'd running sweetly - nice smooth ride etc etc.

But it has this strange 'only sometimes' oil leak. It doesn't happen when it is cold and just sitting - so this is obviously why it wasn't picked up during inspection.

After it has warmed up after been running a while it drops oil - ceases again when it cools down.

It is not coming from rocker cover gaskets as these have been replaced but have not had a chance to explore further and is now dark so will have a gander tomorrow.

Any ideas what the cause might be? Seems to be coming from rear and centre!