I recently got my 9 bolt rebuilt and, and i installed it into my car and added fluid, i recently noticed it was leaking from the pinion seal though a new one was installed at the time of the rebuild. I am waiting for my motor back so no driving was done and i called the guy who built it and ordered and had him install another new one, it is continuing to leak.... anyone have any idea what it could be? something with the housing maybe?

 

When I install a pinion seal I always smear a light film of RTV sealant around the inside of the housing where the seal goes in. Then I drive the seal in. This will seal any scratches in the housing. I also oil or grease the lip of the seal and smear some RTV into the splines of the yoke before putting it on. Oil can leak out through the splines. Then I use red Locktite on the threads, put the nut on and tighten it to get the correct bearing preload.

 

your yoke could be chewing it up also, check it for burs, grooves and such