The car is an '84. I think I know the answer (No) but is there an upgraded bearing available for the pinion? Are the OEM mazda bearings from mazdatrix worth the extra cost over whatever rockauto bearings?

I have to replace my pinion seal so I am going to do bearings while I have it out. I get a bit of a groan in hard braking zones. It has gotten better since I installed a panhard but I have come to accept my diff is just going to need to be rebuilt from time to time.

 

Bearings only alter in precision class - using carefully matched ball sizes, etc. As long as someone's not giving you counterfeit bearings, any reputable brand should be pretty much the same. Rockauto usually mentions the brands when clicking on, the oem ones will probably be NTN or NSK.