The owner's manual for my '47 Diamond T recommends using diesel fuel to clean out the tranny and differential when changing gear oil (on the truck). The tranny is a Warner T-9, non-synchronized four speed. I would not recommend gasoline for the safety reasons.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix