Next time you're under the dash, put the fan on high and check for defrost air leaks between the top of the ductwork and the bottom of the defrost vents. Of the handful of 140/240's I've worked on, none was fully sealed there -some worse than others. The solution is to seal around the base of the defrost vent with self-sticking foam insulation. In one case I also needed to re-position the ductwork a bit by bending the mounting brackets and using drywall screws to secure the connection. Unfortunately it does require a bit of gymnastics to get at this. On our '85 240 I'm sure I was able to double the defrost air flow and it was well worth the effort.

As a note to others on fogging problems. Make sure that the passenger compartment air exit venting is not obstructed. On sedans that means the slots under the rear window, on wagons it's the small grill below the right rear side window. Of course, this will be of little concern to those with rusted out floors.