RB cases (and several other brands) are sensitive to bearing removal when using the OFNA style slide hammer type bearing extractors. There "Press" type or atleast heating the case is the best way to do the bearings.

As said before, the cases are castings and they are not forged blocks, so they are more brittle than billet or forgings. The slide hammers send harmonics thru the casting and will crack the block.

I am not saying this is the reason for your cases being cracked, but if this is how you did the bearings, it is a possibilty. I have never seen two cases in a row that have cracked so, this is just a heads up for you.