Given your description, it needs cleaning. I've got a M48-4 that was doing the same thing, the cylinder release latch was sticking, not moving back when the cylinder closed, and hanging up the hammer. I removed the side plate and disassembled the action, thoroughly cleaned everything and reassembled it, runs like a new gun. If your revolver has been a safe queen, or not well-maintained, old oil and dirt will jam up the close tolerances and make things sticky.
If you decide to clean it yourself, watch some videos on S&W disassembly and cleaning, don't go prying on stuff. I don't know how familiar you are with working on a revolver.