I cannot find this info now but someone posted not greasing drive shaft problem cost him lots of loot to fix. The universal joints on drive shaft are hidden under floor board
Tom
One more reason to purchase and read the operator's manual. iirc though the top shaft and bearings were the weak point of the 3120 and early 3130's. Lame brain operators towing tractors have torn the bearings out of many machines. No oil pump rotation= no lube oil to bearings. Some operator's are also shocked when shown the "tow" position if so equipped.