In the tailor, the back piece Rocket Pack Stealth is not on the list when using the body type Robotic Arm Right. Is this just for me, or can anyone else confirm that it's missing for that particular body type? It's accessible for the others as far as I can see.

Yup. It's missing. I believe it happened when they patched the Jet Pack tp and the new pack skins. That's when i lost the piece from my toons back, who's using right Robotic Arm.
And it's still not fixed....

Still no news on this?

Costume bugs never, EVER get fixed (unless a giant uproar gets made about them). PERIOD.

*points at sig*

a bug that impacts already made toons is worse than a bug that is there from the outset!