Oil leak

I’ve had a slow oil leak since having the bike returned from annual service but I can’t seem to trace it.
The cylinder heads look ok from the sides and there’s no oil coming down from them.
Bit unsure of the two engine bolts at the bottom of the case could be the issue or even possibly the filter?
I also noticed when it was sub 5 deg the drop of oil that sits at the bottom of the block was bigger, which obviously makes sense if the leak is coming from a broken seal.