I can report the following so far.
Knifing the print does not work on this surface. (RC Pearl) I can scrape the dark spot off but it won't take spotall afterwards.
Placing a 'fly' on the spot under red light is impossible. I can't see!
I am not stabbing my film.
Under microscope, I tried to put a "dot" on the neg. Even the smallest spot is too big.
Try to use a needle. Ink won't stay on the very tip.
I don't have a registration system so that isn't workable for me.
I might have to reshoot this....