@
koenbro
I would use this opportunity to upgrade that RD.
You are going to probably need to go to the co-op if you have one near for the special nut and bolt.
One of the venerable Suntour RD's from the time would be much better, they should have a few or someone here will.
The nut and bolt may be difficult to find as many go missing just like yours if that's the case.
I would encourage you to post in the ISO/WTT thread for this too.
You can just jse a regular one in there for now, may have to grind some down but the axle/bolt/skewer hold the bulk in place when clamped, the little bolt keeps it from trying to rotate.
Looks like you are in a pretty serious shop so hopefully you can fab something up.