I have a Kubota 331 mower that has a diesel engine with 1200 hours on it. While using it I noticed it losing power and thought the fuel filters were bad. I slowed it down and it died, I tried to start it and it was trying to lock up. After it cooled it started and ran fine for a minute and then started to labor. I shut it down and put a mechanical gauge on the oil pressure . I restarted it and it had 50lbs of pressure. It started to labor and with the fill cap off of the valve cover it started to smoke as the oil was hot. we disassembled the engine and found all the main bearings destroyed. the rod bearings look fine. How could this happen that the mains are all trashed and the rod bearings are fine. We have many Kubota mowers and a lot more hours than this. I use all Kubota filters and change oil as it should be.