Hydraulic clutch fluid

Just be happy you don't own an original Korn-national -Inter-binder Shout. They use British master/ slave/ natural rubber components, and required special "British Girling" fluid. "Back in the day" I sold auto parts, and we sold a fair number of replacement kits or components after someone with original parts mistakenly used U.S. brake fluid in 'em.

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At least you didn't need Whitworth tools to work on them- still got a box of those buried in a corner of the garage from my BSA/Triumph days...