i have a tip for you...
where the cables go from the boot lid..through into the roof...if this rubber seal is not firmly fit into the chassis...then it will leak as you describe.
i would not spend a penny on new parts until i would find the leak.
its not hard at all..you just have to take some of the interiour out..and have a friend to spray water on your car..while you are in the car...and see where it leaks in.and then..you will solve the problem.

hope you find out where it comes from.

cheers mate