My Super 55 had the same problem when we bought it. The cause was one of the rivets that hold the ring gear to the differential had a head break off. The remaining part of the rivet wandered out and hit the bull pinion and bam, teeth came off. It lost some of the pinion shaft as well. It cracked the differential carrier, so we got a complete unit from a used Super 55. If you get one and it has rivets, remove them all and replace them with bolts. There are special bolts that hold that ring gear on, so it is best to find one with the bolts already in it. Kent Gordon probably has everything you need.