If you are rebuilding a PT pump (like a Bosch P7100 or older PT style), do not cut corners. The three critical components that must always be replaced are:
The Thrust Ring & Buttons: In the gear pump section, the thrust ring and buttons wear out over time. If these are reused, you will lose pressure internally.
The Governor Springs: These fatigue over 50 years. Weak springs cause erratic RPM and surging.
The Shaft Seals: Always replace the main shaft seal and the cover gaskets. A PT pump that sits often weeps fuel from the front cover, causing a major fire risk.
Pro Tip: Always check the "button height" and gear width using a Cummins special tool—eyeballing it will result in low power.