88 5KtQ brake problem

[AV8oR]

Haudi Fellars!
 
I have an 88 5ktq (ABS) that pops the brake warning symbol up when the
brake pedal is depressed and the pedal gradually descends to the floor
(accompanied by a slight vibration). A new brake master cylinder, new
DOT4, and sequential bleeding did not yield the desired pedal stability.

One bleeding nipple broke off in the process and bleeding was
accomplished by loosening the brake line @ the caliper.
 
Any Ideas? ABS maybe acting up? Any BTDTs and fixes?
 
Thx in Advance for any pointers!
 
Zaf - too many Audis