I have a 4th axis for my fadal 4020. the previous owner had replaced some seals as the unit was leaking. it sat for some time before i bought it. i noticed that it was still leaking oil around the back so i took the back cover off and put some RTV gasket sealer around the cover. put it all back together and no oil leak. i then put it in the machine and all seemed good. i turned the air brake on, M60, and heard air hissing out of the back, about 30 seconds later the rear rubber seal around the back of the spindle popped off. not sure what the deal is???