After closing last fall my in ground vinyl lined pool sprung a leak, apparently somewhere near the deep end. The liner is just 3.5 years old. It's a 20x40 inground, 8 ft at the deep end. Most all of the water drained put very quickly except a foot or so at the deep end, and it was too cold to do anything with the leak by then. So, I left it, pulled the winter cover back but only after some of the water tubes had fallen into the pool. Now, the liner on one side is pulling out of the rim/edge in several places. It's still too cold to do much with it. Today I looked behind the liner and it looks like there are sheets of something, plastic maybe, that have folded and/or slid down the sides of the shell behind the liner. What is this stuff, and does it sound like this could be a DIY project as soon as it warms up enough to get into it? Any help is greatly appreciated. This is just my 2nd winter and going into 3rd summer so I still am learning a lot. Thank you!