So I had my rear differential replaced in October last year due to a failed pinion bearing. I was under my car the other day checking the condition of my ACE pipes. I noticed my diff was pretty wet already so cleaned it off and checked again 150-200 miles later. The diff was noticeably wet again and it is for sure coming from the pinion seal.

With it being Easter the garage I used have been closed so haven't discussed options with them yet. Someone on another forum mentioned the diff breather. My only though is that my old diff wasn't leaking from the pinion seal so would discount the breather being blocked. My main question would be, is the seal replaceable without striping the differential?

There were many diff pinion seals replaced due to a TSB on early L494's as they were assembled incorrectly at the factory causing them to leak. I'd have thought a new diff wouldn't suffer from this fault though. As far as I recall there is a special jig the dealers use for setting the preload, it does cause for the diff to be removed, but yes the seal is replaceable, but then the preload needs to be set.

Definitely throw it back at the dealer.