I installed new aerial in my cab before I took it apart. I managed to get my cables through where the loom cables go through, it takes some time to get each one through, but it works. It also took some time to find the cables once I got them through under the dash board.
Good luck?

Yeah I've taken the dash out of a cab. You have to take steering wheel off, pull all the covers off from dash, pull all the switchs out and take the attached cables off, un-screw and take out the dials- be careful not to rip any cables or damage the dial cables..., then un-screw the 15 odd screws holding it in place - 1 at each end of the dash and rest at bottom of dashboard and then you pull the dash off up wards and there are 5 big clips that hold the dash in place - you can't see these as they are under the dash right near the front window area, but it will come out easy.
The leak by the way may come from the heater unit in the middle, if the rubber holding it in place is split water links through - I know it happened on my golf, but you won't see this unless you take the dash off and unscrew the heater unit - which is done via the engine bay area.
It's all outlined in the VW golf maintain books.