Motorcycle and Scooter appreciation

plenty of oil
It's a Bonnie (well a Thruxton, which has sort-of-rearsets, but that bit's the same)

The leaky bit is the gearchange shaft itself, which is a rubber oil seal rather than a paper thing.

I'll give them a call. I reckon they've fucked the seal up when they installed it.

That looks like a double lipped seal (inner side and outerside) and its not been fitted correctly.