I have a 2002 GX335 with a 20hp Kawaski engine. 1100hrs. Tractor runs great as it from day one. My oil pressure light starting coming on but the tractor runs fine. I changed the sending unit, oil, and filter. No light comes on until I mow about an hour or so. What is the oil pressure supposed to be on these engines? I have always maintained it well since new. Any thoughts or ideas will be welcomed. Thanks!