Take the glove compartment out and jimmy rig a folded up coat hanger to wedge open the vent. Didn't take that long and its pretty simple. Of course I live out in SO CA, so the minor leakage is well.....pretty minor.
25 yo cars have rather fragile dash boards. You are liable to crack the dash further by attempting to move it.
If the problem or problems get worse, then by all means you'll need to remove the dash.
But so far I haven't had to replace the evaporator!
