This is quite odd on a Series 2 manifold.

I'm not sure if that type of heat would crack cast quicker than steel..probably the cast.

Well, it turns out the manifold was not cracked, but the gasket on the manifold was shot. Had him go ahead and replace the gasket on the crossover while he was at it. Heck of a difference in performance. Just thought I'd update.

Glad that you got it fixed. Thanks for letting us know what the cause was.