If these are the Mk 2's with the plated wheel rims and the square section axles that may well be the cause of the problem. In the past I have encountered similar problems with this type of axle which is caused as I recall by the axle being off centre to the wheel. If this is the case you may be able to solve it by replacing the wheels with modern wheel sets.
Hope this is of some help.
Regards
Hope this is of some help.
Regards
