Thanks Alec. GL5 is the 'modern' gear oil with vast amounts of EP (sulfur compounds) additives. Earlier hypoid oils (GL-3 and GL-4) did not contain such amounts. Our Triumph gearboxes (and trunnions for that matter) contain brass components that will be corroded over time by the GL5 additives. Thanks to you, I know I don't have any brass to worry about in the diff. If you run hypoid in your gearbox, it is advisable to stay away from GL5 (I use straight 30W non-detergent in my O/D as Laycock originally specified). Unfortunately, GL5 is about all you can buy these days at Autozone et. al. I was able to find a very dusty 5-gallon bucket of the GL4 stuff at Pep Boys that I'll use for my trunnions.