Another option is to square the slots with a hack saw blade and widen slightly so the axle fits while deepening the slot as well. Fill the slot with Magic Stuff poly resin - dries rock hard in 15 minutes. It is much harder and better than epoxy. Drill holes into the poly/original slots - done. Another trick I have used is buy a piece of 1/16 square stock mahogany and CA glue it into the slot. Ca glue the surface around the mahogany as well. Drill your new holes in the original slot. The darker mahogany highlights the depth and position of the original slots. There is rarely anything in the rules that prohibits you from filling the ORIGINAL slots with a substrate. These work great, stabilizes the slot, and allows you to drill straight and accurate axle holes while using the original slot.