Had the same problem. It turned out to be the cross member that actuates the raising mechanisms. The cross member piece had actually bent in the middle. It had flexed so many times that the metal was cracking and it lost strength and would bend and not raise the corners of the roof. The cable pushes in the center of the cross member and it bends in the middle. Eventually it bends and then cracks and starts flexing.
Fully raise the roof and look at the leading edge of the cross member. It it is not straight then you have the same problem as I had. I repaired mine by first straightening it out, then filling it with molten lead to act as a stiffener. It worked good. I was working on it during the weekend and didnt feel like waiting to get a new part. But I would not recommend you do what I did.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k