Cases have been beefed up from the factory over time to reduce the number of cracks that occur, but they still happen. Nothing you can do besides replace the case.
I'm sure they have, but I've seen and have heard of more problems with wide deck Lycoming cases cracking than I have with the old narrow deck ones. Perhaps it is simply because there are more of them out there these days.
Both the new and old cases have their quirks but I'd honestly prefer the old narrow deck ones over new.