My ge authorized repair man said I cannot use the heater kit on my model lss25xg because the back of the dispenser is plastic and not metal. Is this correct? I have not seen any mention of plastic vs metal in any heater installation videos.

Try turning down the freezer temp a click or 2. The water line runs up the freezer door. What setting is the freezer on? Start at 5 and go up if more cold is needed.