As far as I know, Hunter Arms Co. did not use different sizes of rotary bolts, aside from normal manufacturing tolerances. The system was self-compensating. As the bolt and/or the bolting surface of the rib extension gradually wore, the top lever spring would pull the top lever further to center and then to the left.
When I mentioned the possibility of replacing the rotary bolt, I meant that you would have to try to find a good used part with less wear. The other possibility is building up the worn bolting surface on the rib extension. Removing the top lever and rotary bolt mechanism from an L.C. Smith is relatively easy. But putting it all back together can be difficult for even some experienced gunsmiths, so best left to someone who knows all the tricks. The hard part is fighting the tension of the top lever spring when trying to get the bottom of the top lever shaft into its' correct position in the bottom of the frame in order to align the screw with the threads.
Any gun can wear out, and L.C. Smith, Fox, and Ithaca guns with the rotary bolt system are no exception. Factors affecting wear include the type and heat treatment of the steel, the number of shots fired, and also lubrication or lack thereof. Fine grit and dirt in the lubricant can act like a lapping compound over time.
You could try coloring the part of your shells below the primer with dry erase marker to determine whether you are actually getting firing pin drag. Or you could also try switching to another brand of shells to see if anything changes due to harder or softer primer cups. The first step is correctly diagnosing the problem.