Pohill
It is a simple fix, take it to a gunsmith that works on that type of thing.
Before I retired I had fixed 100’s of that type of thing. I no longer do.
It is most likely something that you could do yourself, but you still want
to have someone that is a black powder gunsmith look at it. A good
machinist is not aware of the things that are suitable and available to a
black powder gunsmith and what is proper and safe with firearms.
Some of the advice that you have gotten is good, most is not.
Take it to a professional black powder gunsmith, let them look at it, the
chances are that it is a simple fix.
I won’t post here how I would fix it because I would have to see it to say
and I am [ retired ] not going to be the one to fix it.
I would PM or landline you if you like and give you my experience with
such things but you will still need to take it to a professional black
powder gunsmith to look at it.
Good luck
Tinker2