i have a 1983 cabriolet 911sc, new top installed 2 years ago, the rear wind section is not tight as most are, it seem to be droopy ar sagging somewhat with ripple in window when top is up. the overall fit of the rest of the top is very snug and tight. any suggestions how how to remedy the situation? perhap i'm missing some rear webbing for the side? just not clear on to rectify the situation. it is a very high quality german top in like new condtion. suggestio would be very welcomed. thanks bob