Triumph TR4/4A/5/250 Brake Master Cylinder
Silicone Brake/Clutch Fluid
Unlike normal brake/clutch fluids, Silicone fluid does not absorb moisture.
This will avoid corrosion in the system (and under strenuous braking conditions tends not to boil).
Also, it won't harm paintwork if spilt.
Note: Before filling with Silicone fluid, the entire hydraulic system should be flushed out.