Rear differential fluid service, wrong fluid?
Wife took the T-bird into an independent shop, where they replaced the rear diff fluid (it was overdue, car was at 120k mi).
While they put in the Ford Motorcraft 80w90, which the manual calls for, they didn't add the friction modifier. Since she has the XE rear, that's a problem.
Here's my question: Can I simply drain out a little bit of fluid with a pump and add the 2 bottles of friction modifier? Or should I try to drain out as much as possible and add the Motorcraft 75w140 that dirtyd0g recommends?
I really don't want to take the cover off, I figure that they got all of the old fluid out when they had it off on Tuesday, so even if I don't get all of it out, at least it's new, clean fluid. Is it ok to have the two different viscosity oils mixed though?
Last question, why do I always do my research *after* it's applicable?