check crankshaft end play---it could be that your thrust bearing has suffered excessive wear from riding the clutch, bottoming out of the clutch or no free play in the linkage--any of these will kill the thrust side of the bearing ( and sometimes not the crank, other times, crank also)
Its possible that a partical of the copper/brass stuck the relief valve open, causing your low pressure reading---
How is your
oil system plumbed and where is the
oil pressure taken from???