I really appreciate this thread.
I was about to change oil in all four places (diffs, xmission, xfer) and stumbled over here, wanting a quick reference to determine how much to buy for my '96 4Runner. It has 413,000 miles, and was overdue for my third or fourth change. The oil in the transfer case had developed a bit of that obnoxious burnt smell. I had never thought about the GL-4/GL-5 issue, and had gotten used to rather stiff shifting, particularly into first gear.
WoW what a difference the Royal Purple GL-4 synthetic oil made. Within five miles of driving I noticed a tremendous improvement in shifting. The transmission feels so smooth, at times I almost forgot to depress the clutch.
I ended up opting for the RP because I could not find Amsoil easily, and the Zone carries RP -- at $22/quart. I hesitated to pay $90+ (with tax) for four quarts of this stuff and felt like I'd made a big mistake heading out the door. But now, I'm here to tell you guys, heed the advice -- get the GL-4 -- and you won't regret it.
