I have only skimmed quickly through your post. (I got lost in your swapping axes.)
Anyway, a machine that old is going to have brush type servos and these can give the over current alarm simply because carbon dust from the wear on the brushes cause short circuits. A possible quick fix is to dismantle the servos, blow all the dust out and reassemble them. If this works it is not a long term fix because the servos are probably going to need new brushes; or new servos.