sweet... From time to time we hear of a manifold cracking. Like any other part of a vehicle it MAY crack. However it does not appear to be a weak link in vehicles such as yours. One thing to remember...we don't hear about the millions that DO NOT crack!
If I was on my third cracked manifold I'd be looking at what was different on my vehicle that was not on other guys vehicles.
Several things might lead to helping the manifold to crack.
HAving the pipes tied down tightly so thay cannot MOVE with the rest of the drive train might help the manifold to crack.
OR having the engine/tranny on broken or loose mounts may also help.
I would imagine having a restricted exhaust system might help build up heat and also might cause such failures.
The common crack that we see here is at a weld on the manifold. MAny of the guys here have welded the crack and put the manifold back in service...with no ill effects.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />