It smells like gear oil apparently, so my 14yo son tells me!
Checked under the rubber boots at the engine end of the shaft tube and no oil so that's one thing.
Had a real good look and it seemed like the leak may have been a rally slow weep from the drain plug.
It had a badly fitted copper washer under it.
Removed, drained and used a fibre sump washer for sealing, re filled and we will see.
Maybe that is all it was.