Basically brake parts cleaner WILL disolve finish as you found out,but that's all I ever use now to blast insides out from powder fouling residue,as it does same job as gunscrubber but at fraction of cost. but then you already knew that. As to finish,the best you can possibly get is offered by brownells,is epoxy based,and is called "acra-coat". The main bad thing about it is it takes 3 whole days for each coat to dry. Another finish I use a lot of is also offered by brownells,and recently midway too,called custom oil. As you probably guessed by now,you'll NEVER be able to match the old finish exactly where it won't be noticed by sharp eyes. Anyway,what you do is airbrush it on,rub between coats,repeat as neccesary 15-20 times. For that old browning,use the gloss. If you don't have access to airbrush/air compressor with dryer (dryer is IMPORTANT!!!),fret not-they also offer it in aresol.