all st141 coronas seem to rust at the bottom corners of the windscreen, and at the base of the fuel filler opening.
also check behind all four wheels, as there is usually a build up of dirt and other crud that gets damp and causes rust.
the gregory's manual doesn't say anything about sedans and wagons having different diff ratios, however the autos have a 4.11 and the manuals have a 3.89 ratio.