Hi BB, you're quite correct in saying it is a common problem....it is a design flaw in the later Scotties with the adoption of the twin rail engine deck....previously all machines had a solid deck and no probs.
Just to clarify, not all rail fatigue fractures and cracks are caused by clutch out of balance problems, I have seen small cracks radiating from the engine attachment holes because of the Briggs inherent engine vibration.
All Scotties, to my knowledge, had the captive cotter style of the inner clutch half up until the production the Rover 45, and subsequently all after market replacement clutch halves have the opposing grub screw arrangement.
