I was told at Rotax repair school in Canada that the fretting issue was caused by one or maybe it was more of the through bolts that held the case halves together. These bolts allowed the case halves to "work" and the fretting issue became a leak. The mechanic would sometimes tighten the case halves and induce a binding of the journals on the crankshaft itself. At least thats the way I remember it. If you call Rotech Research in Vernon BC and ask for Mike or Rob, they will straighten us all out.

I have 700 hours on one and no fretting.