Hello, I'm having an issue with my welder that has the Kubota v1505. I was using the machine and one day it shut down and the oil pressure light came on. It cooled down and when I restarted it the oil pressure was at 75psi (good). As it runs its starts to creep down slowly until it shuts off. I haven't been using it regularly until recently so could it be old oil and a bad filter? It has about 5k hours. Any help would be appreciated, thanks!