Water on fridge shelf - ice in back of freezer

Water on top fridge shelf below freezer. Took off back panel in freezer, defrosted pool of ice over drain hole. Used salt and hot water to clear ice dam in drain tube. Have done this 3 times. Problem returns after a few weeks.

I need to find out how to troubleshoot the issue and if I can effect a DIY repair.

Any experts out there? Wife about to make me buy a new one. Hate to fill landfills with repairable appliances.

Thanks,
Bill