Are you certain it's not a bad rag joint on the drive shaft? Those were neglected on every 123/126 that I've owned.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.