I haven't gravity bled the system since the problem first started. At that time I was able to get a trickle at all four corners, but I'm not sure you would call that good flow. Should I re-bleed the system with the gravity method? I'm not sure I understand your next question, bear with me! Are you suggesting removing the pressure line before it enters the ABS unit to compare fluid flow under pressure between this point vs. at a wheel cyl.? If that is your thought I'll give it a try later today, let me know and THANKS!