Until about a week ago, no problems.  I had a complete brake job last
year.

I noticed recently that the brakes were taking longer to stop.  I just
figured I wore the pads out again, I drive a lot and am somewhat led
footed.  But going home yesterday, the pedal on the truck would go most
of the way to the floor and was very spongy.  The truck would stop but
the harder I pushed the pedal, it didn't seem to change how fast I was
stopping.  Kind of like stopping a ship at sea.  On the way home, the
ABS and Brake light both came on.  I stopped and found that the master
cylinder resovoir was almost empty.

I stopped at a local shop and had it checked expecting to find that I
had a leaking caliper at 98K miles.  The mechanic looked at it and said
he didn't see any leaks on the front or back and that I had 70% wear
left on all of my pads.  He felt that the last people who did my brake
job might have bled the brakes but not refilled the tank.

When I left, the ABS light and brake light were still on but he said
that the ABS unit needed a few miles to get filled back up and that it
should go off.  The brakes seemed better but still not normal.  I drove
it to work today and the lights are still on after about 40 miles.
Braking is back to being terrible.

Any ideas?  A leak he didn't notice?  A bad ABS unit?

Thanks,
Michael