My name is mike, I work at Napa and I could not for the life of me find a replacement pinion seal with all of my resources. finally i broke down and called Campbell Nelson nissan in shoreline wa and was able to get the o.e. seal p/n 38189-U3001 ordered. now that i have there seal and part number i was able to cross reference there number to a napa 13978 NOS. this is an skf seal from NAPA auto parts. this number on the package is different than the number he gave me on the phone otherwise i would have crossed it earlier and ordered my own seal for half the price.
so to recap
o.e. 68-73 510 pinion seal p/n 38189-U3001
Napa skf p/n 13978 NOS