I just got me a 94 integra and every time I start slowing down when press down on the break pedal it gradually goes down slowly. I also slammed on the breaks yesterday and the front driver side locked up none of the rest did. anyone have any suggestions on where to start

 

brake fluid good?
vaccum hose to brake booster good?
break booster leaking?
mc leaking?
correct pads installed?
prop valve leaking?
brake line leaking or pinched?