[V8] V8 Heater control valve

[bob moy]

I was replacing the heater supply hose this weekend and notice that the 
heater control valve was also leaking.  So I lookup the valve on the 
internet and notice that there are two.  My 1990 V8 Quattro have the vacuum 
valve, but I did notice a blue connection that could be used for the 
electronic control.  The electronic valve control is about $57.00, while the 
vacuum control valve is around $35.00

Do anyone know which model year the switch from vacuum to electronic was 
made?  I'm guessing that the 1992 and later used the electronic control when 
they went to a different climate control.  Also would the control valve from 
a Audi 100, 5000 or 200 worK?

Thanks
Bob