Having a recurring problem where after moving at a decent speed for a period of time, the oil pressure light comes on when I go back to idle speed. It doesn't happen when I start up and idle out past the breakwater (about 10 minutes), only once I've been cruising for a bit and then slow down. Pressure gauge reads 20 when I throttle back to idle speed. Oil was changed and level is good. Could this be a bad sending unit?