MTD Yard machines lawn tractor, how do I add oil to the gear box there is no filler hole?

Model # 13ai675h062





Serial # 1b131b30253





I have checked the manual and parts list for a filler hole but none is shown in the diagram or listed on the parts listMTD Yard machines lawn tractor, how do I add oil to the gear box there is no filler hole?
It's sealed. You have to replace it.....Like most everything else on an MTD.MTD Yard machines lawn tractor, how do I add oil to the gear box there is no filler hole?
Maybe you don't have to add any to it.