Now you have made me curious, too... I am tempted to dig in to mine, vs fit an electric fan. (Must resist another project... Must resist...)

Links for your perusal...

Refill of viscous fan clutch pictures

http://www.benzworld.org/forums/r129-sl-class/1474495-viscous-fan-clutch-theory-operation.html

Jaguar V12 Fan Clutch

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Looking for Early 108 windshield surround wood in decent-to-good condition.