I was given a rifle by a friend in similar condition. He had hunted with it, shot it three or four times during season (with Pyrodex RS), never cleaned it, and just leaned it in the corner in his basement for a couple months. He was down there doing something, saw it leaning there, and considered it junk. So he gave it to me. (after he told me a fantastic story of how one of his nephews must have done this to his rifle.. which I did not believe).

I spent days on that rifle. I removed the barrel and shot the barrel up with brake cleaner. Then I put the breech end in a can and plugged the nipple. I then filled the barrel with motor oil. After a couple days, I poured all that out and started cleaning the barrel.

I went through a couple brushes, and a bottle of bore solvent, and still got rotten looking patches. So, Ilapped the barrel with NAPA valve grinding compound. The strange thing is, it still throws a dark gray patch from time to time, but no rust. And with 70 grains of powder is a good roundball shooter.

Best of luck with your medical condition...