I had to replace my cable outer on one of the rohloff control cables, both small hex grub screws on the bayonet fitting rounded, holding up the job while i sprayed penetrating oil onto it at periodic intervals over a day. My vain hope being that i broke the seal.
The problem here is the alloy the bayonet is made of, you get a reaction with the steel of the grub screw and being small you cant get enough torque on a hex key to break it, hence rounding.
I went to an extreme after failing with the oil.
After protecting the frame; went to the bayonet with my small pencil flame blowtorch on a low flame setting, after 30 seconds heating i got the pliers onto the bayonet to get the hex key in and the bayonet.......melted in the grip of the pliers. Onto the phone to sjs for a bayonet fitting, you get both halves, seems unless you do coat liberally in copper grease, these parts are consumables.
I had a similar metalalurgy experience in the 80s with a 2nd hand vitus aluminium frame that had the h/bar stem frozen in place, making it non-adjustable!