davids2toys Dave Redline sell GL-4 in all different weights from 70/80 up to 80/140. It's about 13.50 a quart Goggle it, there are alot of places Autozone has a 20% off if you order it on the web look at Redline 50204 and 50304. The other one is
Amsoil sell gallons and quarts of 75w-90 api/gl-4 (MTG) Prices vary and its a full syn. If you have a GM store check part # 12346190. This is a GL-4 BUT might have friction adders. Try tightening the bolts on the tail shaft housing, this may top the leak depending if it's a gasket or rtv leaking. Happy holiday Rick L.