I have the same problem. Only it's never been in the mud. The picture of the gears are not visible in you post. Could you resend them? I can use reverse if I sit the machine off. Grab and hold the right hand break. Put into reverse then turn on the key and start the machine in gear. This bypass a safetyNo, no codes. Just grinds when I try to put it in reverse. It eventually goes in if i slam it in to gear.