bomb or master cylinder or power booster

[jjwjr@ix.netcom.com (JEREMY J. WALTERS JR.)]

I drove my car again after your suggestions, brakes work fine at first, 
 while sitting at a stop light, pedal sinks toward the floor, though 
not all the way.  After letting off the brakes and coming up to speed, 
the pedal returns to the top and is fine again.  The only time the 
light comes on is when pushing very hard on the pedal, then it vibrates 
and the warning light comes on, then goes out.  I just don't wan't to 
replace good components unnecessarily.I am still confused by the 
conflicting advice from many of you!

Thanks!

Jeremy Walters
San Ramon, CA 
86 5000CS