Other than cleaning the barrels and cylinders/pin, I haven't disassembled or cleaned the innards of either my Henry, Remington 1858 Factory conversions or 1887 going on 4 years now...I do plan to get to it this winter
I've been shooting BP in 45 Colt for 9 years. I use only Winchester brass because it is supposed to be the thinnest.I started out downloading with cream of wheat and the guns were in need of attention after about every stage so I tried full loads. Guess what, even worse because there was more fouling with the heavier load. Tighter crimp....never noticed any change. I went to .454 and I did not notice any change. Then I started annealing my 45-70 and thought I'd try the 45 colt. What a huge difference it makes. I shoot full load 45 colt under a Big Lube J/P200 bullet (.452) through my '60 Henry and I get virtually no blow back. With un-annealed cases I would have to spray the carrier with Ballistol after every stage. Now I never spray it and my maintenance after a match is to wipe out the carrier area with a patch wet with Eezox....that's it, it's clean! I shoot about 30lbs of Black a year in all my SASS guns so I do run plenty through them. I upgraded to an Annealeez 2 years ago and haven't looked back. Annealing does help with the pistols as well. Without annealing I would quickly get fowling in the head space area of the frame which would make cocking difficult. I still get some fouling but I can make it through a match where before it needed attention every stage or two.
So that's how I control fouling during a match. As for cleaning, the pistols get the cylinders removed and just get how water in the sink being careful not to get a lot of water into the internals. Barrels get a few swipes from a nylon bore brush, a mop then jag patched with Eezox. Cylinder/pin gets greased with Mobil One red grease and assembled. A squirt of Ballistol through the cocked hammer area to lube the innards and then the whole gun wiped down with an Eezox patch and then a clean cloth. The '87 gets a rubber stopper pushed into the breech and the Windex squirted down the barrel before filling it with hot water. That sits while I clean the barrel of my Henry with a slotted jag carrying squares of Windex wetted paper towels. Usually one paper towel ripped into 4 squares is enough. Then the barrel and carrier area are wiped with an Eezox soaked patch. By now the '87 is ready, the water dumped and up to 4 of those same sized paper towel patched rammed through the barrel with the last one soaked in Eezox. The receiver section get's a squirt of aerosol Ballistol. That's it, 30-40 minutes tops.