Side by Side Maytag Frig/Freezer Frig not cooling

Question

Model is MSD2356AEW, about ten years old. The coils in back of freezer
are icing up bad. Thus frig is not cooling properly. I suspect the defrost
mechanism isn't working? Is this a costly fix? Any other possible reasons
for what causes this? I've been removing the inside panel and using a hair
dryer to deice the coils. It's only been a week and they are iced up again.

Due to the age of the appliance, I'm wondering if it more cost-effective to
fix it or just purchase a new appliance.