I have a M1916 Spanish Mauser. The problem is that the safety cannot be set. The only way that it can be applied is to pull the bolt sleeve out a bit farther. Would the problem be the firing pin spring, or the firing pin? Any help would be appreciated.
Try swapping out the safety and/or cocking-piece. Also, the trigger-sear could be worn, if it is, it won't push the cocking-piece back as far. If it only lacks a few thousandths of engaging, you can use a dremel tool to re-shape the lead-in ramp on the safety, and/or grind a chamfer on the mating portion of the top of the cocking-piece.
The firing-pin and/or firing-pin spring are not the problem.