On my WM20, the breather pipe in the back of the oil tank attaches to a rubber hose (65-2060) which then connects to a brass tube that is attached to the left hand gearbox plate.
Hi Danny. I hope this helps. In the photo the rear mudguard is on the right, chaincase on the bottom (fuzzy) and gearbox on the left. The vent tube is in the middle of it all.