Good Evening,
I have had a closer reread and I think I was mistaken last night, ignore my comments.
To start again. I think we all need to be clear on the use of terms, particularly 'arm', it seems to drift.
This black plastic piece is what I will call the 'crank arm'.
View attachment 102080
Notice the central piece that drives the potentiometer is broken off with this example.
Further this is part of the manifold and not a separate part and hence not available separately.
Yours appears to be broken at the top right where it links with the vacuum actuator arm. If this is the case strongly advise to buy A2Steve's used lower manifold.
I too have embarked on trying to remove this crank arm for copying. My exploits so far...
Andy