IMHO the Firstline brand is OK.
You don't have to stick any brand when topping up the brake fluid,
only the DOT numbers must match. But if you remove the master
cylinder, there will be not much brake fluid remain in the brake system
(about 10-15 ccm if we didn't look the clutch cylinders). If the brake
system wasn't air/oil tight then the brake fluid was able to absorb humidity
from the outside air, which is lowering the boiling point of the fluid,
and can lead to corrosion inside the brake system. Therefore i would
recommend to evacuate the remaining brake fluid from the system during
the bleeding process.
You will need about 0,7-1 liters of brake fluid (depending on the
evacuation method), a transparent hose which fits to the bleed valve's
head, and a vacuum pump or a syringe (which fits into the end of
After refitting the master cylinder top up the reservoir. Depress the
brake pedal fully 3 or 4 times to flood the inside chambers of the
master cylinder. Top up the reservoir again if necessary.
During the bleeding process don't let the reservoir to run dry.
Pick a brake and connect the hose to the bleed valve's head, then
connect the vacuum pump or the syringe to the other end of the
hose. Loosen the bleed valve. Operate the vacuum pump until you
see bubbles coming out from the bleed valve.
With syringe pull it's plunger fully, then gently tighten the bleed valve.
Disconnect syringe, empty it, then reconnect. Loosen the bleed valve,
and pull the plunger again. Repeat the process, until you see bubbles
coming out from the bleed valve.
Top up the reservoir, and you can move to the next brake...
With the process above you don't have to bleed the brake force corrector
valve separately, the pump or the syringe will suck out the air from it.
I've performed this on my 33 successfully twice when replaced the brake fluid.
I hope this was useful.