Never heard of soaking a motor in nitro before. First off, tear the power head apart completely. Inspect for wear on the piston / sleeve, Conrod ends and crank pin. If any of those show any wear, time to replace. Look at the end of the crank, is there "L" or "13" stamped on it? The "L" is a 12mm while the "13" is 13mm. You will need to know this for bearings. Bearings most likely should be replaced with quality Swiss bearings, see Ron at RaceCraftBearings.com ... To get the bearings out, turn the oven on to 350, put the crank case and PTO pieces on a piece of aluminum foil and put in the oven for 10 mins. Remember those are still hot, use gloves
to take them out of the oven. The bearings should fall right out. If one stickes on the crank, use a bearing seperator and pully to pull it off. The carb may need to be cleaned up a bit also. The only part that needs to be lubed is the flex shaft. Sounds like it's still fully lubed. As for torque, use blue loctite when reassembling it all. Give all the bolts a nice tight snug fit. Doesn't need to be cranked down. If you turn the starting cone over, the prop should also turn. If it doesn't, then the flex shaft is most likely broken. Could be the prop shaft is broken..

This should be a good starting point. Come back with any updates or questions...