somebody mentioned door locks and that got me to thinking that maybe some of
the 1980 and 1981 folks don't about this:

in the 1980 and 81 models (don't know how late in the 81 model year), the
passenger's door had a lock mechanism that would allow the door to be opened
from the inside (by pulling the handle) EVEN if the door button was pushed
down (locked). this was a bit of a safety hazard, as we found out one
afternoon when a 4-year old opened the door as i was driving down the
highway! luckily, he was belted in and the door was pushed back against the
bus by the wind.

but there is a fix! :) you can get the door lock mechanism from an 82 or
later, or find some dealer that has some of these laying around  ... it's
part number 251-837-016A ... it's the A on the end that makes the
difference.  it is a very very simple replacement: two large phillips-head
screws. this is NOT the part you put the key into, but the brass-colored
square box thingie that you can see easily if you open the door. it's on the
rearmost edge of the door and is the part that latches onto the
brass-colored part that is bolted to the body. you just undo the two big
(and i do mean big) screws, wiggle the mechanism loose from the key-related
part, put the new on onto the key-related part, and put the two screws back
in. that's it. it hooks onto a little thingie that the key-part turns ...
and it's easy to see how it fits and put the new one back right. total time?
maybe five whole minutes. ten minutes if you want to look a lot and can't
turn the big screwdriver :)  i paid $25 for the part waaaaaaaaay back in
1982 when i had an 80 bus, but i'd bet any 1982-1991 bus in a junkyard has
the same part.

hope it helps. good luck!
joel