hi bud, i have a 93 pajero, same as a montero different name, i had the same issue, person i bought it off never tried to fix it.
door never opened when i got it. i took the panal off with the door in place. just has clips around the outside, remove the tool tray, take of the door handle and plastic bit around the door handle that opens the door and remove panal. you should now have access to locking mechinisim. easy job, fixed mine start to finish in an hour. mines a jap import but assuming they're similar.
this is where all the clips are in yellow
and the lock mechinisim, mine was stiff and just needed oiling to get it working again