John:
The front ones are at the bottom of the door lock posts just ahead of
the pinch weld. The rears are inside the black engine air grilles. Take
out the grilles and carefully lift up the bottom end of the black
plastic hose.
I prefer to blast them out with an air hose towards the sunroof (up),
with it open. You will probably get a gob of pine needles, decayed
leaves, organic waste. I find this routine maintenance to be necessary
every few years. Many will find it necessary more often- mine sleeps
every night in a closed building.
Yes, my 82 diesel is a sunroof. Good thing, too. Makes it a lot more
tolerable in the summer and this 1.6 NA diesel could never pull A/C plus
the  3500 lb. of stuff in this van sometimes!
Al Brase
69 double cab, 82 diesel