Oh! That kind of bolster
,,
That's what I got too,,sidelock cappers..I use pipe cleaners,,ya know? Them fuzzy little wire things smokers use to clean tobacco pipes? Their flexible,,you can cut'm with a scissors,,and the fuzzy part holds lube for reaching those hard to get places. Cheap and disposable too,,$2 at any smoke shop or drug store gets ya a bunch.
I guess I don't worry too much,,after cleaning and lubing the bore proper,,I remove the clean-out screw and run a lubed pipe cleaner in that hole as far as it goes,,then I just allow the viscosity of lubrication to cover the rest,,(lube flows!). I usually use a rubbing alcohol bath after water cleaning to help remove moisture,,then use LPSII or Hoppes#9 for long term storage.
I don't want to turn this into a "lube" story but I stopped useing BB,and found out years back that WD-40 causes rust.
I know I'm using the dreaded oil product on my BP guns but I remove all the oils before shooting with "break cleaner". I'm the kinda guy that cleans a gun till a white patch comes back white.(is there another way?)
I'll go to a weekend vous', or on a hunting trip and just do "field" cleaning the whole weekend and shoot just fine,,but when I come back to the cabin I'll spend some time and do a thorough job of it.