I just dug up my first M4 Early prod. and got it almost done for the museum, but...the auxiliary generator regulator "ghost silhuette" doesn't appear when trying to assemble it on the chassis. I have the part in my inventory and I even crafted one (so now I have 2 of them), same problem. I verified the game files and still the glitch persists.
I've renovated all of the other M4 variants - excluding Jumbo - and they've worked fine.