On an old F**d truck I had,I checked the tranny oil sshortly after I started driving it and it was so empty only a pintof gear oil drained out of it,so I put a full can of STP in,and topped it off with 90 wt. It not only made it ALMOST quiet,it shifted easier (4 speeds no syncros),and the rear seal leak slowed to less than half of what it was leaking before.I also put a piece of heater hose on the gearshift from the floor boot to the shift knob;that rid me of a harmonic ringing that bugged me at about 65 mph.
Speed