On my 46 I disassembled and cleaned the pan cake at the diff. and it was fine,(shifted diff with a vise grip a few times to loosen it up after many years) . Then I installed all new vac.lines. My vac. rotary valve is a sealed unit and was leaking also. Then while the engine was runing I kept shooting WD-40 in the line and let the vac. suck it up to the valve while fliping the lever around. It stoped leaking bad and now stoped leaking completely! That WD-40 is great stuff!
