S&L bolt
The S&L bolts are very simple units. The screw at the rear of the bolt unscrews (may require a gun vise to hold the bolt), the firing pin, firing pin spring and possibly a spacer to create tension on the spring are the only parts inside the bolt housing. I have found the bolt housing usually collects a bunch of gunk - depending on how well the previous owners maintained their guns. A general cleaning and oiling should help.