Choose carefully. Amsoil SG gear oil is NOT safe for the yellow metals in our synchronized trannies, for instance. Other Amsoil products may work (Series 2000?), but no one carried them in my area, and I really dislike the infomercial-like Amsoil marketing, so I didn't want to run it anyway. Most GL-5 gear oils have sulphur and/or phosphorous additives which we can't use. Mobil1 LS is GL-5 rated and CANNOT be used either. I got that straight from the Mobil1 1-800 customer support number, since I see so much conflicting information about whether it can be used. Call them yourself.

Unless it's multi-rated, don't chance it. By the time you notice a problem, it will be too late. If it is multi-rated, it will say so on the bottle.

Penzoil Syncromesh is a good one and widely available. I love Royal Purple; when I switched to it I noticed a huge improvement in shifting smoothness. One reason I moved away from Redline is that no one carries it in my area, so I would have to order online if I needed to top it off or change it. That's reason enough for me when other good alternatives are locally available. I don't think switching from RP will provide an improvement based on my experiences with different gear oils, but flushing out your tranny and putting in fresh oil might help. I drained mine after just one year, and it was pretty contaminated.