I've had a bunch of 21's apart. The basic disassembly is pretty straight forward including driving out the pin for the trigger sear levers. The hammers, opening lever & locking bolt are another matter because they take some specialty tooling for compressing the springs. You may want to just take the stock off and then thoroughly clean & lube the action the best you can without disassembling it any further than necessary. If your still getting light strikes after that, I would suspect a broken hammer spring on that barrel. The spring could be broken and still function but could cause light strikes.
