As I discussed in another thread, on a real ABH-6 helmet, the oxygen masks are attached to metal buckle things on either side of the face opening, and those in turn are held onto the helmet with little round rivets. Since the X-Wing helmets are vacuforms of those, the rivet translates as a little bump. (also, see the screw on the left side of the pic? That secures a strap that goes behind the wearer's neck. Those screws also translated to bumps on the X-Wing helmet.)
Wellllll, due to some quirk in the process when creating the helmets for ANH, that rivet bump is NOT PRESENT on the wearer's left on the film helmets!
Now, it LOOKS like it's there on Luke's, but it's just painted on, to match the genuine painted bump on the other side.
So I decided it needed to go on mine!
I couldn't just sand it down without filling it in on the inside, or there would be a hole.
I used a technique I learned from the "Modelmaking Guru" channel on YouTube. He makes a substance he calls "sprue goo".
You cut up a bunch of tiny pieces of scrap plastic or sprue from your kit and put them in a bottle, fill it up with MEK or similar plastic weld solvent, and wait. The plastic will dissolve into a single thick globby mass you can paint on, essentially becoming liquid styrene. If you use plastic that came from the kit you're working on, the color will be a perfect match because it IS the same plastic.
In my case, I already had some made, so the color wasn't a match, but the helmet was being painted anyway.
So I glopped a bunch on the inside of the unwanted bump:
after curing, I sliced away the bump...

...and then, as always, sanding and filling. In theory, filling wouldn't be necessary if the glop filled in just right, but, you know....
Anyway, skipping ahead to the bump-free surface:

Which isn't 100% invisible. My concoction cured as a slightly softer material than the surrounding plastic, so it was impossible not to oversand. But it got me close enough that it isn't terribly noticable after painting (and standing back a few feet

).
