The B3, reverse piston is rubbing against the K1 drum, because the reverse clutches are worn or the reverse clutch clearance is to loose, causing the B3 piston to over stroke, rolled lip seal, rub marks. Check the B3 clutch clearance .060 to .080’’. Adjust the clearance by changing the steels they are selective, also buy the updated B3 clutches and colane steels.