All of the problems I have read about to date, to my thinking, seems to come from the use of modern cleaning agents & solvents. I fail to see why anyone would bother to try & fix something that is not broken! A method that has been working for over 300 years, but it seems that muzzle-loader users are getting lazy; they don't want to use the old tried & true methods because it seems too arduous & time consuming. So they turn to simpler quicker methods.
Some facts: When you oil the bore of your gun, pistol or rifle, the barrel absorbs some of that oil. If you use a modern solvent or cleaning product it will remove that oil from your barrel. Then you will have to purchase some other modern product that promises to stop your barrel rusting after you have cleaned it!
The best method is the oldest method, clean your barrel & lock with boiling water, dry the barrel with cloth or some other natural plant fibre. If I have a fire going I usually let the barrel stand where it will warm but not get too hot. Next, using a natural plant fibre again I oil the barrel & lock with sweet oil or neetsfoot oil. Job done. If you are seeing signs of black on your cleaning cloth, then you have not washed the barrel sufficiently. DO IT AGAIN! If you are getting signs of rust on your cleaning material, it can be because the wash water was not hot enough, or you did not dry the bore sufficiently. Keep running oiled material down the bore with your ramrod or cleaning rod until the bore is clean.
There is such a product as water soluble engineers oil, my Father called it "Pigeon's milk"! This product is what my Father told me to use when cleaning the barrels on my guns, this is what he used on his guns. The same method was used as in these videos, but the water soluble oil was added to the wash water, just a small amount. I have not used this oil since I was a lad, but it worked well back then. If it is the right oil, it will turn white in contact with the water.
Take care out there.