First, check that the engine side clutch half is actually loose on the PTO shaft when the cotter is loosened, and the captive cotter pulls quite a distance into the clutch half when the cotter nut is firmed up. Please post pictures of the PTO, the bore of the clutch half, and the cotter when it is assembled and clamped up. At that point Deejay, our SB45 man (and very proud owner of one) will explain how to examine in detail for some of the internal symptoms inside the clutch. To answer your immediate question, only the engine side clutch-half, and perhaps the key and the thrust bearing, are likely to be damaged. The later style of clutch-half is unlikely to give trouble if correctly installed - the design weakness was overcome in the later design.
