[Zero10]

I changed the gearbox oil to a cheap GL4 synthetic, and drove it for 3-4 months before putting in the Amsoil, but the old transmission fluid was almost like caramel it was so thick, and it just stank! So I figuried mine needed some extra cleaning. For the most part, you should just drain and fill with the new stuff. I'm sure there is some way to flush it, although it may not be very easy to do.

I also am skeptical of the one-GL-fits-all claim, but I really like the results of their wear tests, and I have seen them backed up elsewhere, so I am inclided to believe them.
The one thing that does worry me, is that the series 2000 gear oil is a LIFETIME oil, as in, never change it. That sounds like a terrible idea to me. Maybe I'll double the drain interval, but surely not lifetime.

I don't know if Amsoil is worth the extra bucks for putting in the engine, but I found it pretty cheap in Calgary, so I decided to chance it. It is staying much cleaner that the Mobil 1 did, but it's also a much thicker oil.

I heard about that adhesion issue before, but the last time I heard of it was about 10 years ago. From what I understand, all the good synthetics adhere to the metals, so even when there is no oil flow, there is still librucation. To help prevent damage on startup. I could be wrong though.