Remove the front panel on your Performa and look at the area where the transmission rests on the base for any signs of oily or greasy residue. This would indicate a bad lip seal leaking on the lower end of the transmission. This tends to make the snubber ring greasy and slippery, causing the tub not to stay balanced. Also, lean the machine back and pop the white plastic cover off the center pulley to see if there is evidence of oil there. This will confirm a bad seal.
If no oil is visible, then the snubber ring may be the only problem, although you'll need special tools to do the repairs on this machine. The snubber ring rests under the brake stator, which has to be dismantled to do the repair.