Mileometer Problem VW Golf Mk3 Conv

Hello, I have a Mk3 Golf Conv. When you get in it, you see the Mileague and you can pree the button to change to trip. All normal so far, then you start the engine and you get CErr------ and ---------, basically nothing until you switch off. VW want £360 to fit a new one, however I think/hope there must be a simple fix. So firstly I am hoping someone can explain a) how I can get to the 4 screws that hold the unit in without wrecking the dash, and B) should it be plugged in upside down or which wire goes where? Or C) is there something even easier to sort out the problem. Many thanks.:1zhelp:

this thread seems to be in the wrong place;)

Moved ;)