So the membrane is circular, that's a relief. I thought it was a teardrop kinda deal with a large surface area.

Is it something simple enough that a female mold for the face and sides could be turned on a wood lathe?

I'm thinking along the lines of:

squirting silicone caulk into the mold with excess built up . . .

. . . letting it dry . . .

. . . cutting the excess off the flat(?) backside . . . erm . . . flat

. . . peeling the finished part out of the mold?

Is the original part cast around the solenoid, using it as the core of the mold?

Can it be? That might make it even easier to make replacements. :?:

Just spitballin' here, never saw or touched one IRL, obviously.