Motorcycle and Scooter appreciation

Since I got my Triumph back, with new left side engine cover and gear shift, it's been leaking oil from the shifter when parked.
Is this just because they have overfilled it or have they fucked something up?
The shaft, case, and seal ought to be new.

Usually if the gasket is not a new one, it will leak. However after engine work it can leak for a few days anyway. Give everything a good wipe and have a look. Bring it back to the mechanics if you can so they can check properly.