Unfortunately inside the bolster is hard to check. If you pour solvent down the barrel you could watch and see what color the solvent comes out as. But I really know no way to check the inside of the bolster. Even if you take out the bolster clean out screw and insert a tooth pick to see what comes out. Since we are talking side lock, I would definitely not leave it loaded for extended periods of time. I did this with my Renegade one year.. And finally I was on stand and in walked the first legal buck (very small spike) that I had seen in over 10 days. I took my bead, the cap went pop.. and no boom. I even got a second cap on the nipple and again.. pop. Well the buck went bye bye. I finally had to pull the nipple and drizzle powder down the nipple port, using a nipple pick I worked as much powder in there as I could, and put the nipple back on. The next cap fired it. At a tree stump. And I loaded immediately and tried it again, and it fired. So I am guessing the powder was compromised somehow during the storage. After that I stopped leaving them loaded.

I would fire the rifle off.. then use a hot soap and water bath to really flush that bolster. And after that pour some alcohol down the barrel. And let that drizzle out the bolster. Then you could oil that up and set it up right, any spare oil will work down there.

At least a bolster can be replaced.