I"ve noticed when i looked in the rear view mirror of a 91 nxs that i test drove, that the overhead liner was sagging, center rear by rear window. I pushed it back up hoping that it would snap back in place but it did not. How do you fix this & anybody else have this problem? It is only sagging at the edge, center, about 1/4" down & 6" wide. Any info would help. THANKS