Toyota: Heater Water Control Valve (VSV)

Couple questions regarding the vacuum control valve (VSV) which controls the
heater core water flow on a 1987 Toyota Supra Turbo:

1) Is this thing nothing more than a electric solenoid driven pneumatic
valve?

2a) If "YES" to 1), what should the coil resistance be? I have two of them
(both bad) and one reads about 630ohms, the other about 750ohms. If they
are nothing more than solenoids, what is the failure mode? (**) I just had
my second one fail (after about 10 years since I replaced the original).

2b) If "NO" to 1), what is it exactly?

3) Any idea of current prices? In 92-93, they were about $110US from the
dealer (I got my first replacement for about $20 from the junk yard).

4) Any suggestions for sources or alternatives?


(**) Both of mine just quit working. Coil is obviously not open or shorted
(maybe somewhat shorted!). Took one apart and cleaned it. Verified
pneumatic paths were clear.

Any ideas will be appreciated!

Thanks!

Don