The big issue is that if any ballast/grit gets in the bridge motor teeth or the rim rail, the turntable may lose alignment and sometimes just goes dead. Normally doing a 'zero' will fix this, but if the turntable was really 'jumping' due to the fouled gear teeth, it may loose electrical contact and just go 'dumb'. If this happens a complete power on reset/zero/re-program the positions may need to be done.
After cleaning out the gear teeth on the rim and bridge, we vacuum the pit and the 'hole' where the bridge fits into. We then 'formed' the wipers that contact the bridge a little higher so that they may good solid contact even if the bridge jumps due to ballast/grit still in the gear teeth.