Platinum Racing Products - Nissan RB Crank Shaft Packing Washer
Have you noticed your timing belt guide rubbing up against your oil pump seal and oil pump?
It gets it hot with friction and damages both the pump and the front crank seal.
Nissan RB block thrusts are all cut in different places from the OEM manufacturer, and other than trying to make some type of spacer, or remove the oil pump gasket there is not much you can do to avoid having a problem.
This simple little precision EDM wire cut 1mm hardened shim may be your answer, suits RB Twin Cam and Single Cam engines.