GL-4 vs. GL-5

[3Q Jay]

didnt see anything in search on this. i know gl-5 is NOT recommended for nissan mtx, if i remember right, something in gl-5 attacks metal in the synchro's. but here's my question. the fsm specifies gl-5 as diff libe for the q45. is gl-5 truly necessary or is gl-4 sufficient. i'm thinking of going to synthetic at next change, but it looks like [not an exhaustive search] the sythetic is gl-4 [not 5] rated.

[maxnix]

Mobil1, Amsoil and Royal Purple all produce GL5 synthetic gear oil.

[IvoryJ30t]

use GL5. gl4 will cause excessive wear of the ring and pinion.

and GL5 is not recommended for almost any manual trans with synchros.

[3Q Jay]

right, thanks for the replies. I found 85W140 M1 at shlep boys on Sat, and indeed it was GL5 as Brian said, but i opted to find 75w90 instead, which they did not have. so, i'm still looking-may try autozone today. I'm assuming that the 75w90 will also be gl5.btw, i agree about the gl4 in mtx, as i always used that on the old maxima, interesting to note that every bottle i saw yesterday, both dino and synth and mix-synth was gl5 rated.is this a plot to destroy synchros.....