Timing covers are not part of a rebuild. They're normally reusable. When I rebuilt my engine, I decided to buy new ones for cosmetic reasons - and to have fresh cover seals. The only place I know to get them is from a dealer and they're fairly expensive.

You either had a bad bolt or it was over-torqued or the threads not properly prepared - it's probably impossible to determine the cause without metalurgical analysis.

No locktite should be used on the bolt. The hole threads in the crankshaft nose should be chased and the bolt threads and washer face lightly oiled with engine oil before installation.... then torqued to 131-137 lb-ft.

Frank