Ford 1700 losing oil pressure

[1drobi]

This tractor only has the warning light, no oil pressure gauge, but light seems to be operating correctly. Goes out immediately when tractor is started cold and stays out at even lowest idle. But as tractor warms up the light flickers on even at 1200 to 1400 rpm. As I run her back to put her away (worried), the light comes on full even at 1500 to 1800 rpm. I switched to 15-40 oil and it seemed to help for a while, but the condition has worsened lately.
Do I need a new (or repaired) oil pump? How difficult is it to replace? No New Holland dealer near me, and I wonder if I can trust just any JD or Kubota shop to take on the task?
Any comments appreciated!

 

[Kenny G]

I know that this is a long time since this was posted but had the same problems years back.. I cured the problem by changing oil filters. I tried a Fram filter it was too restricted went back to the Ford or NH worked fine after that