4 speed transmition oil

Years ago a Chrysler Tech Rep told me that even tho they came from the factory with ATF in them that the dealers were suppose to change them out on the first service (somewhere around 1500 miles) to 80-90 gear lube and the guys who race and have "slick-shift" setups were to use ATF but expect a slight leak on the side cover and the tail shaft. Since my tranny is regeared and slickshifted I have used ATF in it for the last 15 -20 years with out a problem (I pull it apart every 4-5 years to check things out) and the only thing that has needed replaced was the input shaft bearing. I tried 80-90 in it once and you can't shift it fast without it grinding a little - and forget power shifting without the clutch ...it ain't gonna happen...:) So I went back to ATF