You know it's guys like you why this world is so screwed up , guessing your a service guy in a Kubota dealership who screw people every day ! Sorry no one could answer my question ! Good luck
No Flip is not service tech, but there are a couple guys on the forum who are, and who could give you more help when they log on, white tiger and lugbolt. My computer is down, so I can’t access what info I have on the diagnostic codes. There are not a lot of folks on here with the newer M tractors with common rail engines. I have an L which does, and would like to encourage you to proceed with caution looking at the fuel line. It could get very expensive if you or your buddy make a mistake. Please don’t start trying to crack injector lines, it is dangerous to you and not a good idea at this point. The new engines are a different breed of cat from your standard old style diesel.
It sounds like you have fixed the oil filter gasket problem and it is now holding oil. Is that right?
Other than the p0340 code, does your dash panel look normal when you power up? No other lights?
When you turn the ignition to the first position, on but not crank, can you hear a ticking noise which is the electronic fuel pump?
It may be that you just have to clear that code to get it to start, but if the water separator is not filling it might be a separate problem.
Do you have a shop manual for the tractor? There is a procedure for clearing codes and trouble shooting in most of them.
Let us know the answers above, there may be more we can do to help. Expensive tractor, don’t want to give bad advice. Hoping the loss of oil did not damage engine, but hard to tell over the internet.