Quote from zray
quote:
You are not using synthetic gear oil now are you? I understand from David Kee that the Toploaders don't really like synthetic oil and were not designed to run with it.
http://www.davidkeetoploaders.com
they certainly weren't designed for it as synthetics didn't exist back then, but...... When I mothballed my T-10 I put in a toploader that D. Kee had restored for me & initially used conventional gear oil. When it came time to change the trans. oil I decided to try Mobil 1 synthetic gear oil. It works fine for me. The warning from D. Kee states that it does work fine for some people, but not for others. The problem is supposed to be when shifting fast, the synthetic oil doesn't provide enough friction for the gear syncros to work properly. Apparently I'm so old I can't shift fast enough to induce this problem so I'm sticking with the synthetic oil for the reduced wear benefits.
Z.Redline synthetic gear oils have different formulations for trannys than rear ends. The I've been using their MT-90, GL-4 spec, in my original close ratio T-10 for at least the last 15 years with great results. It has friction modifiers that allow for proper synchro function so (driver) age is not a factor. 
http://www.redlineoil.com/product.aspx?pid=46&pcid=7