Yes, your heater core is probably leaking, a very common problem. It is very easy to replace. A phillips screw driver will get you to it and about the only other tool necessary is a pair of pliers for the hose clamps. There is no cable for the valve, VW's idea is that you lift the seat and manually move the lever, though you could make a cable control if you really wanted to. Ceck for power at the motor first.

Mark