If you take the Axle nut off can you rock the drum on the Axle? what happens sometimes when the Drum is loose it is constantly moving on the axle splines it can wear the splines on the axle it happen's more often with German Drums because the metal is harder then the cheap repops that wear the splines in the drums are you useing early or late axle nuts? I Use the Late German Axle nuts on Everything, the late nuts have the flanged washer built in also if you useing the early axle nuts they have no built in washer and when loose it tears up the snout of the Drum.which makes them come loose
Friend of mine had this problem. After replacing the drums a couple of times he realised the drum splines could rock on the axles and replaced those as well - no more problems.
The drums definitely fit sloppy on the axle. The last drum I installed, I inspected the axle and it did not look damaged. The only thing I could think of is that the axle spline is undersized. They are Sway Away Axles, so I would assume they are the right size, but who knows. I have a set of stock axles, I will double check the size.
Oh yeah BTW I have pampered these drums, no burnouts, or rock crawling.