Quoted from dug:Could be something as simple as the flipper shaft is binding. Lift playfield and loosen the pawl nut, make sure the flipper shaft is slightly (1/8") raised as tighten down the nut. You can use an old credit card and cut a slot in it to get the proper gap.
Likely this above.
see around post #17 in this thread
https://pinside.com/pinball/forum/topic/right-flipper-sticking-stern-acdc