We had a similar problem with the fins frosting up from right to left, it was determined that the problem was the door seals and to replace the seals Norcolds answer was we had to replace the 2 doors as they do not sell seals for this unit. We have since replaced it with the Samsung RF-197, very happy with the extra space and the frost free. Space wise it fit the spot the Norcold came out of we removed a small useless flip up cupboard that was above the old fridge.
Barry and Glennice, Kit and Kaboodle (Lhaso Apso's)
2008 Winnebago Tour WD, GMC Terrain toad