BRAKES

[AL24@domain.elided]

I usually just lurk and read ,but I have a question concerning brakes. I have
a 79 Scout 100k 304 auto, and lately the brake light comes on and the pedal
will go down while sitting at a light. If you release and reapply the brakes
the light goes off but the pedal still slowly goes down. It doesnt feel like a
cylinder so I was wondering what the symptoms of a bad booster are. It has
been doing this for weeks but my son forgot to tell me. Next question, if it
is a bad booster are rebuilts available or is it off to the wrecking yard, and
are they year specific? 
Thanks Al Lampson