AG liner to return seal questions....Please

Hello everyone!
I have been a lurker around your forum for a couple of years now and I have learned alot. I decided to signup because you seem to have a great community here with lots of knology and I also have a problem.

I have a AG pool that has a problem where the return goes through the liner. Over the winter the liner has pulled away from the return at the bottom exposing about 1/4 to 3/8 of an inch of the metal wall below the ring that holds the return in and breaking the seal.
Every year in the fall I drain the water to the return level then remove the pump, hoses and filter to store them in my basement so they dont freeze. Is this the cause? Maybe the sand under the liner has settled and needs more even though I don't feel a dip in the bottom? This pool has been up about 5 years with the same liner and has never had an issue before. Is there a return with an oversized collar that will fix this? If not, what would my options be, if any?

Thanks in advance, Chris