What do you guys recommend for gear oil/weight in a new Moser 12 bolt for break in and after break in use? The rearend has a Eaton posi. and Richmond gear. I have also been like valvoline products.

AAron,
I dont set up a bunch of rears but use nothing but Richmond gears when I do. I have been using Richmond's synthetic gear oil and have had absolutely no problems in any of the ones I have set up.

http://www.richmondgear.com/01pdfs/OILVID.pdf

I use Redline synthetic in mine since having it built last summer...12 bolt with 800# carbon fibre clutches in a brute strength unit with Moser axles.
Plus, no posi additive needed.

Amsoil. it is good and available all over the place.

I know allot of new guys run synthetic like Amsoil and have had good luck, but Eaton does not recomend synthetic oil with their posi units. I have a 12 bolt with an Eaton posi. I just changed to synthetic oil myself, but have not seen any benefits so far, it sounds and operates exactly the same so far.