I have a 20+ year old Kubota G4200 hydrostatic trans lawn/garden tractor. Runs great! The manual calls for 10W-30 oil which I have been using since the beginning (I use Synthetic). It does'nt state anything about deisel spec oil. Should I change to a diesel spec oil this late in the game? Which? Also, if you will forgive me I have asked in the past about oil filters for this engine as an alternative to the official dealer filters but I am not sure yet of the correct number for cross referance to any brand at this point. Thanks for you indulgance.