A friend has a slight lube leak at the joint between the torque tube and the rear end casting on his 47 half ton short truck. Maintenance Manual shows the tube pushed into the casting and riveted in place. It makes no reference to any servicing of this connection. The lube level in the differential is correct and lube is not leaking from the transmission past the Oakey bushing. Have any of you experienced this problem? If so, what did you do to resolve it?