As a temporary maybe permanent repair, remove the fill plug on the tranny and smell it,stink like hi sulfur gear oil?Have you changed the gear oil lately? If so,drain the oil, refill with straight 40 engine oil,use quality detergent oil.In some cases, modern GL5 gear oils impair synco action on tranny not designed for it.This assumes the torque tube seal is ok and the motor oil won't find it's way into the rear end.
