If the engine's output shaft (PTO) is not exactly in line with the center of the sprocket bearing, there is going to be a problem. Yes, the sprocket bearing is self-aligning, but the crankshaft main bearing isn't, and the clutch-halves are rigidly bolted together and cannot act as a universal joint. If there is a basic misalignment of the two ends of that shaft, the machine will adapt to the situation by deforming the engine mounting rails at their least-rigid point, which is the inboard engine mounting bolt-holes. That happens to be right where the rails crack. Over time, the bore of the engine-side clutch-half will tend to wear and become loose, which may reduce the deformation and stress of the frame rail. Unfortunately if that clutch-half happens to be a setscrew type, this loosening probably won't occur and the rail cracking may happen sooner than it would with a captive cotter type, which seems to be rather prone to becoming loose on the crankshaft over time.
I think we need to hear a lot more about this reported misalignment of crankshaft with sprocket bearing. If it is a common problem it would not be hard to fix, but it would be better to do this before the rails crack.
