II have been using cotton buds,with lighter fuel to clean all wheels,which is effective. I have just noticed on an on line vid,that the current is tranferred - not from the wheel running surface,but from the inside edge,nearest the loco frame.I appear to have been lucky in wiping this area when cleaning ....

When reinstalling wheels, use a very fine pointed tweezers to hold in contacts onto the inside of wheels flanges, not difficult.

I pull bogies apart & chuck then in a small container of lighter fuel (very cheap by the litre from hardware shops) & shake built up residue off.

Your loco would have had to done a 1000 km for contacts to wear beyond practical electrical functioning use. Swap contacts with boring locos, or otherwise buy new parts

But really, even flogging a loco to death, contacts still function.