Hydraulic clutch fluid

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...

LOLOL Every once in awhile I remember the term "Whitworth." I never owned such a vehicle, but in my Navy days at NAS Miramar, there were a couple of guys working on Brit stuff at the hobby shop.