Thanks for your replies. The differential seems to be adequately filled and the transmission is pretty close to full (top gasket around the shift is seeping). I'll address that later.
I went looking for that breather on the axle housing. It's missing and the hole was plugged with many years of road crud. I cleaned it out and it looks to be an 1/8" pipe threaded opening. Does anyone know where to get a threaded replacement? I haven't been able to locate one. They are referred to as an axle vent or rear differential vent, correct?
Hopefully, this will solve the problem. If not, Hotrod Lincoln suggested a thorough power washing with an engine cleaner and a layer of silicone-type sealer (RTV) to the joint where the tube meets the differential housing.
Thanks again,
