I don't mean to be too critical, but I haven't seen a lock like that since CVA was making really cheap guns back in the 1970s. There is no bridle over the tumbler and if you don't have one then your trigger pull is going to vary from shot to shot. Also, the tumbler can rub against the lock plate hindering its fall. JMHO, but a lock isn't worth a darn without a tumbler, and not worth having. Dump it and find another lock. Even back then CVA also made a good lock with the bridle. Maybe you can find a used one somewhere.
One thing nobody mentioned - you could replace the nipple first. Or check it to see if it's still nice and flat on the top with a sharp edge. If not try filing it flat. A sharp edge is needed for the cap to go off every time. When shooting pistol matches on the national range all day, we'd replace the nipples anytime we started having troubles with ignition. Then in the evening while sitting around the campfire cleaning our guns and drinking some adult beverages, we'd dress em back to good. Good luck.