Yep!! go for it! I have an 89 and it is a solid car. Its extremely reliably enginewise and is a great little car. Easy to park, fun to drive and fairly comfortable. The master cylinder wouldnt be too hard to replace. I recommend that you upgrade to a better one than stock though as braking isnt the cars strong point. (look around this forum, there was recently a thread about upgrading brakes.)
If the car is in good shape otherwise, i highly recommend you buy it!
Do it!!! These cars are extreamly well built and it has a fuel injected engine so you won't have to worry about the crap carbs on earlier Sentras. If everything else checks out fine, for $300 you can't go wrong.
i would be a little leary if i were u i have a damn nice looking 90 model that i got for 200 plus my camero which was a piece of well any way my motor makes a god awful cladder/ knock so im going to buy a 97 monte carlo hopefully