Jassper,
Well done.
Out of curiosity I've often wondered how a viscous clutch fails.
Weak bimetallic strip over time?
Worn out entrance pin-valve?
Worn out exit valve?
Loss of silicone gel?
What are your feelings after having resurrected one with fluid/gel replacement? Is there a failure mode you would call primary? Or do you feel it's a compilation of several factors over time? I know your sample size is "one", but that's more than anyone else.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)