The only reason to rebuild would be to keep an original AC marked part on the motor. The new units are not marked with the AC logo or part numbers.
That and the company that makes new units, Airtex, is a gamble... and these are made in the USA.. hahahaha so they MUST be high quality. NOPE.
I got a great price in a new vacuum fuel pump that was defective out of the box
https://www.tm9-801.com/forums/viewtopic.php?f=26&t=1609&p=3386&hilit=pump#p3386FLAPs would not honor the original sale price on the return (I could have went warranty return, but decided try and swap it at the FLAPs.
Since I have an original AC marked unit, that will get rebuilt so I knows it done right.