Does the fluid empty? Mastercylinders are netorious for leaking out the back and therefore into the passanger compartment. Best be being that you dont really know a whole lot of history being that you just recently bought the car is to go ahead and change both components (preferably OEM toyota units) and some good fresh DOT 3 or 4 fluid. A little more costly, being OEM and both, but a better piece of mind knowing that both are new and OEM.
The reason that I say OEM is cause I personally have had bad luck with aftermarket ones and know of a few others that haven't had the greatest of luck either. Spent the money for toyota ones and haven't had a problem since. Thats just my oppinion though.