Hopefully one of the Larry-s will join in. I've heard from more than one person that the case and sump bolts are just grade-8 automotive fasteners. I have no inside knowledge if it is true but I can assure you those fasteners are stronger than the parent material of the components they are joining. Would be fun to test the OEM component properties versus the grade-8 locally sourced ones. Maybe the OEM fasteners get some extra quality checks; maybe.
Would case fretting be less of an issue if Lyc used close tolerance bolts joining the case halves or at least removed the threads in bearing?