I know this has been discussed enough, however, is there a year in which merc changed the header on the 525 motors so as not to have any problems with cracking? Most manufactures do updates all the time as they see things fail in the field. Secondly, if you have 525 motors, should you just chuck the headers and replace them before they cause any motor problem?
thanks

I believe it was 04. As far as I know, if the outer tube goes all the way to the flange, it is the old style. If the outer tube does not go all the way to the flange and stops short and is welded to the inner tube, then it is the newer version.
About the same time, they also changed the head bolts and gaskets. The older ones had GM head bolts and gaskets and the newer ones have ARP head bolts and Cometic head gaskets. Hope this helps.
Eddie

If that's the case, I think I have the newer style. Can you tell from this pick? Looks like the outer tubes stop before the flange.

your safe,those are the newer ones. but they still crack and when they do it sounds like a leaking header gasket..