Well, since SSC didn't have replacement heads, I rolled the dice and ordered a regular figure in hopes of replacing the head on my EX that had the defects.
The regular came today, and from what I can tell the whole figure was in good shape. So, I just replaced the whole figure and boxed up the one with the defective head, so as not to risk breaking the head/neck pistons. These figures are almost certainly the same between the EX and regular, with the accessories being what's different.
I'll sell the replaced figure at a later date so I can get my cost back, to someone who missed out and has a home for a needy terminator.
So, I think we have a happy ending here.