I have a Bachmann Locomotive 4-8-4. It doesn't run but I hear the motor working. The rear drive wheels come off. I took the bottom apart and found that someone greased it up real well. I am in the process of taking the grease off. How do I keep the drive wheels fastened so that they will mesh with the motor and run. Shold I try gluing them? There are no splines and the fitting is too loose for any "press fit. Any ideas?