This is my 1st post......I've been told by every supplier and expert that a 1979 Spider uses 15" blades. I bought the car with blades that get stuck at the top of the swing. I called a supplier was assured I needed 15" blades and they get stuck also. I am now going to order 13" blades. Does the 79 model year have a mix of 13" and 15" blades? Any help would be appreciated. Thanks.