in a nutshell..

-vc were and are rebuilt by some companies in europe and  the US
(actually not sure who in US)
- fill amount is crucial as you noted below. but filling accurately
is theoretically doable with some thought :)
-seals are available
- some experts state that when vc is high mileage, microscopic burrs
on the internal plates are worn down. these burrs are supposed to be
important in torque transfer but the exact role they play has not
been explained.
- many vehicles use vcs, but I have never found a part # cross
reference.
-they all seem to be in the same price range, give or take a couple
hundred bucks :)
-you can test function on a lathe after refilling

alistair

On 3-Apr-10, at 10:50 AM, neil n wrote:

Right. Gee. You'd think DC et al would make their "mix" public.   ;)

I assumed VC fluid fill was standard fare for Syncro owners. Seems
just getting part out can be a challenge for some. (looking quickly at
samba posts)

Even the quote below from
http://www.vanagon.com/syncros/technica/vc-expert-interview/index.htm
would scare me off:

"The percentage of air in the viscous couling is critical, and the
percentage is almost always a low of 80% and a high of 86%. He said
that if you went above an 86% fill then you would have the VC
activating on the highway during normal driving and a dangerous
situation would exist.    ........"

I wonder if a VC from another common AWD vehicle could be made fit?
Maybe one where knowledge of filling accurately is more prevalent?

Neil.