Pull the small electric plug above the gear change out.
This will allow you to pull the black cover at the rear off.
Just above and to the right of the large pulley is hex head bolt… remove this to add oil to the gearbox.
There is no oil level indicator… ! (except when it comes out of the bolt hole…)
Put the plug bolt back, and reassemble.
Mine doesn't seem to leak oil, and I haven't refilled it for ages… must do so again soon..
Hope that helps!!
Alan