Tim gave you some very good advice about the fluid. Alot of people do not understand the importance of fresh brake fluid. Also, if your brakes start to feel a little mushy, change the fluid. You should find that this solves all your problems. Once you have fresh fluid in your system, it is not necessary to drain the whole system as long as you maintain it periodically. Here is the method that I use with great success.
1)Remove the master cylinder top.
2) Bleed off brake fluid, as if you are trying to remove air out of the system, until the fluid is just above the brake line hole in the bottom.
3) Refill master cylinder with fresh fluid.
4) Repeat steps 2 and 3 one more time.
I do this every 2 or 3 races and I have absolutely no brake problems. This method also prevents air from getting into the system. I use EBC brake pads front and rear with Maxima brake fluid.
Hope this helps you out,
Gary