I just wonder how big of a problem this has been since there must be 10's of thousands of these motors out there. I guess I am just concerned since I just bought one with the 706 casting. Should I nip it in the bud and go ahead and replace the heads now? I do have another question that may be easier to answer/talk about. Are all the 706 heads made by Castech? Or is that why you have to look inside to see the Castech marking? I know I have the 706 cause I can see it clearly on the outside of the head passenger side.