Barry, i bet it a mis-adjusted linkage.  go under the bus and turn the
spline joint by one spline.  See if the does it. If not, turn it the other
way one spline. That fixed it for me.  BTW, the spline joint (in my 84
non-syncro generic bus) is behind the gas tank... so that is about the
same location on the bus where the sliding door/passangers front door
closes against (but under and center of the bus).

Hope this helps.
_matthew
ps, there could also be a few more issues, but this is the cheapest and
fastest to fix.

Matthew Pollard          "Racing with the wind and flirting with death
Dept. Of Chemistry        So have a cup of coffee and catch your breath"
University of Idaho
www.uidaho.edu/~poll7356