I'm afraid you're right, and that I will need professional help, but I'm avoiding it as long as I reasonably can. I hate that I have no way of extracting ABS codes myself.
I don't quite follow your explanation of the purpose of the hole in that "bolt." Are you saying it is some kind of a relief valve? It doesn't connect to any of the 3 brake lines. When the brake fluid squirts out, it shoots almost straight towards the fuel filter next to it.
I wouldn't be surprised at all if the caliper slides were binding. I may just take the rear calipers off and service them without replacing the pads. That parking brake return spring is a lot of trouble to get back on though.
I have looked at the whole system and the only leak I've found is at the aforementioned "bolt."
Also, my ABS light, after a day of not flashing, has resumed flashing. In what ways can the ABS system adversely affect the normal braking system? I can only think of 2: the loss of power assist due to a failed ABS pump (not a problem for me, the pump is working) and the unintentional restriction of brake fluid to one or more wheels due to a stuck/inoperative solenoid. As it is now, I can detect no flaws in the operation of my brakes from the driver's seat.