Look near the hinge on the door and see if the door itself is cracked around the hinge . My 89 with 275K was cracked at the hinges and made slamming the door necessary to close the door . I found some nice low mileage power doors with proper power mirror mount holes in the proper color and swapped them .
       You could also try rubbing the seal down with Talc powder or Silicone   Spray to help ease the door closed . 

-Stacy