Eric, that is an interesting idea, but i don't think I would like to experiment with a good motor.
Your original comment of that is the price we pay is probably the easiest way to live with it. Put a tap in the oil line?

If it becomes necessary to repair the pump, I think the best way would be to hone out the piston bores in the rotating body to ensure it is round. Then have a hardened steel rod centerless ground to whatever the OD needs to be. Cut the rod to length and radius the ends on a belt sander.
The body and pistons were probably made from a hard grade of metal, which i don't think would wear much, as long as it was kept in oil.

I would think the most wear would occur in the cast iron pump body where the piston body rotates.
This is an area where the hone round and build up the piston body with hard chrome would work. You would only need to chrome the surfaces that meet the cast body, then grind to size.
Either of these solutions is a fiddly job, and probably not worth the effort unless you absolutely had to restore a pump. In another 50 years, it may become a standard process if nobody ends up manufacturing new pumps.