When unscrewing the 2 screws holding what was left of the clutch rod boot into place on my 1967 04D NOR Camaro, I noticed it had a steel retainer and a boot underneath. I didn't think anything of it until I realized the NOS gm boot simply wouldn't screw into place using the retainer.
After some digging, on UPC 7 C2 of the aim, there is a design change.
1st design being 2 pieces with retainer part #3886688 and seal part # 3886686.
This design is replaced with part 3909071 that is the one piece.
Interestingly, although my car is 04D the change is dated 10/26/66.