Hi MowingManiac
These engines are very hard on oil - have seen many fail. Could have been bar oil but there is/was a brand of mower oil that was blue/green.
There is often a plug on one side of the gearbox
I have the mtd trimmer attachment version which I think uses the same reduction box and it has a plug on the RHS, but is actually filled with some sort of nlgi 2 moly grease. I got given an older attachment as well so I split the case, scooped out the old dried cracked grease and refilled
