Had a problem with my oil pump idler gear recently. It’s plastic and was causing a whiring noise. It was so tight on its shaft that I had to prise it off with a heel bar. Fitted a new one and the noise has gone. My concern is the cause. So I have checked the oil pressure. Manual says 13 psi at 1600 rpm and 36 psi at 6k. Mine is 20 at idle and 75 at 6k and if you hit the limiter it’s over a 100psi. I have checked the relief valve and spring length and all seems good. My question is, is this normal or have I got a problem that has caused the failure of the idler gear. Do these plastic gears swell for any reason.