£10.99+vat from me
I race on this stuff, and tried many makes of "performance" fluid to cure my boiling brake problem. RBF600 was used and it went away, so I have stuck with it and their performance oil products also.
 
can you just "top up" brake fluid if needed or do you need to replace the whole lots so its all the same product?
 
Depends how old it is anyway. Brake fluid needs changing every 2 years as it absorbs water which boils making air bubbles when you brake hence brake fade. Best to change it all anyway as you know it's done then. Doesn't take long to do with the right tools.
 
jus had a full change at seat few months ago but the warning light keeps coming on for low brake fluid levels
 
The light is also used as a brake pad sensor ,if fitted, and the handbrake switch. Make sure your pads aren't getting low or your handbrake switch sticking shut. If it is loosing fluid, check the bleed nipples. If if is leaking you should notice if the pedal drops when depressed. I had a Mark 2 escort which the cylinder was leaking. Problem was it was leaking it into the car so no visible puddles under the car.
 
thought the pads sensor light glowed up amber and was a ring with dashes around the edges?? also the pad sensor light beeps once, where as fluid light beeps 3 times intermitantly.