You might want to us a "motor oil flush" aditive. They have them here and I feel they work on old motors that have set. I also had a Ford F800 with a Ford 6 cyl turbo motor (ex US NAVY) that had low oil presure. I flushed the motor and cleaned the sending unit and it was fixed!Same as you Carlo, I don't have any leaks and no oil spewing out anywhere. Originally, when I got the truck last year, it showed over 60 pounds. Then it scared me one day, went pegged the gage at 120 PSI and stayed there. Then, it suddenly dropped to 0 (zero) pounds. At that point, I figured the original set had give out. So, I ordered a matched gage and sending unit. After that, it showed around 80 or so at startup, then after it's warmed up good, hovers around 60 PSI. I have not absolutely determined what engine it is, but I'm pretty sure it's the Continental. It has been replaced, in 1995 according to the data plate, with an entirely new engine. Has the "D" turbo, and the "thick deck" block/head arrangement. Really good running engine.
My Duramax diesel runs at 60 PSI cold, then when hot, it drops to about 15 at idle, and 30 at 1500 RPM, and 50 at 2500 RPM. Go figure.....but the dealer says that is correct.
It bothered me the first time driving my M35A2 with the high reading but I remember my Dad saying if it really had high presure it would be blowing it out every where. I have almost zero blow by. On the other hand my 923A2 has low presure by design. This took me some time to get used to!