Kenmore: freezer working, refrigerator not due to frozen air return...replacement needed?

I have a Kenmore Coldspot (model 106.57022601) side-by-side refrigerator. About a couple of years ago, we had a problem with the freezer working great, but the refrigerator not working. We called a great repairman who found that due to a faulty thermostat/heater, our evaporator coils were frozen, which blocked airflow into the fridge. He fixed it, and everything went back to normal.

This happened again about a week ago…when I put my hand up to the inbound airflow duct (which blows cold air into the fridge from the freezer) and felt no air movement, I suspected a similar problem. We couldn’t find our former repairman, so we wound up going with a new one (big mistake, but that’s another story). Anyway, to his surprise and ours, the evaporator coils were actually fine: they weren’t frozen, and there was no ice-buildup. After hemming and hawing for a while, the only thing he found was that the lower, return-airflow duct (from the fridge back to the freezer) was frozen up with ice. He used a hairdryer to thaw it out and, after also cleaning our condenser coils at the bottom of the refrigerator, started things back up.

Things now seem to be working normally…there is cool airflow coming from the inbound duct again, and the fridge is cool. However, now my family is suspicious and are pushing the idea of a new refrigerator. From my research, I found that frozen return-airflow ducts typically result from faulty door seals (I used my hand to check…we don’t seem to have that) or possibly from folks not shutting the door properly (which has happened on occasion). Now I’m wondering: is there anything else I’ve missed that could have caused this? More importantly: is this a symptom indicating that our refrigerator needs to be replaced soon, or do we just need to be a bit more careful with our fridge doors and replacement is something I can wait on? I deeply appreciate your input…THANKS!