I've bought a couple of revolvers and shotguns with the same problem and cleaned up several other. In fact, I look for revolvers with that problem to pick up cheap. Can usually pick them up for a decent price. What I've found is people have used WD-40 to clean and lube them, squirting the stuff into the lockwork. The liquid carrier evaporates leaving gunk. Take them apart, clean out the WD-40 gunk, lube and good to go.

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183rd FBINA