I have the same RC2072 for about 10 years now. I have a clutch to try and avoid shearing the 1/2" bolt. Have sheared it 4 or 5 times in pretty rough service anyway. I have replaced the stump jumper pan and even launched a blade. Bolt in tack blade split at the hole(Never found it either)...
I have the same mower. The single nut you show is suppose to be torqued to 325 ft/lbs every mowing season. A torque multiplier is a great tool for this. My small torque wrench only needs to go to 75 ft/lbs. Do not oil those bolts unless you want to loose a blade! I threw a blade once (and...