I've had the Audi valve for almost 7 years now - zero problems, the heater works just fine...the chance of it disintegrating and leaving me on the side of the road pretty much nil (I would say never but you never say never...)

Sam

 

Answering my own question.
Bought this Four seasons 74671 heater control valve on Ebay.
Bigger than the original valve, but fits OK with the original hoses.
Works better than my old plastic valve, better closing.

 

so how often does the valve down there have to be replaced ??

 

Mine was 7 years old when it blew.