Replacing a heater matrix on a B4

[Audiden]

I suspect my heater matrix in my 1995 80 Avant is leaking as when ever the heater knob is off the cold I notice a drop in the level of coolant in the expansion tank. As a result I don't use the heater at all, but rather than face a winter in a freezing cold car I'd like to know how to renew it.

I've heard that its a 8 hour 'dash out' job but the mechanic that changed the matrix in my old B4 Coupe a few years ago did the job in 3 hours? He initially told me it was a big job & would take about 7 hours & hence would charge 150.00 (dodgy garage that I won't be going back to). He did the job in less than half the time but still charged me for 7 hours labour!

Any help on how to fit it would be much appreciated.