I have an old Mainline J72 which had been in storage fort years and all the axle spacers were split at the ends so the wheels slipped out of sequence and jammed when I tried to run it.
I flooded the hole in the spacers with thin super glue and then soaked away most of the excess with the point of a twisted peice of tissue. Once the super glue had gone off the wheels were a tight fit again and there was no wheel slippage. Fortunately, the split had not extended across the gear wheel.
When I ran it again it still jammed even though the wheels were not slipping. The problem seemed to be that there is so much play in the wheels and tie rods that the lead wheel set can still get out of sequence. A liberal oiling seemed to cure this, and although a bit jerky at first, a good 15 minute run seemed to sort it out.
I can't guarantee this will be a permanent fix, but superglue is a great gap filler and if you use the thin stuff it will easily find it's way into small splits.