Don't know if relevant or what but three of us at Tong Jeepeyfest rogered our starter motors in the same deep mud pit, prob seems to be if you stop in the mud which was deep enough to come through the right side door opening (36" or hip high) the motor will compact with mud.... fixed mine with 4lb BFH the other Jeeps were not as lucky starter motor and alternator had to be replaced and the third Jeep had clutch issue.
Only thing I can suggest is removal of starter motor after serious mud... and wash and lube.... Don't know if that has been your prob?