There are lots of different opinions out there on oil brands. Mobil 1 synthetic ATF comes pretty highly recommended as fork oil. I would assume it would work well in the rear as well? Everyone seems to have their own preference with tranny oil. Mobil 1 synthetic 5w50 is good, 15w50, 10w30, Castrol syntec 5w50, pretty much any regular motor oil will work. Most manuals will recommend 10w30 or 10w40. It doesn't really matter too much what brand. ATF type F is also used quite a bit. The ATF generally needs to be changed more frequently, but it's a little cheaper. Basically, so long as you change tranny oil regulary (every few rides), you can take your pick on what to use.