2003 RFront caliper locking intermittently

Wife's car, started about 1mo ago. Replaced caliper, rubber brake line, and abs wheel sensor. Checked wheel bearing-okay.
Pads and rotors-fair, I am not going to replace until problem fixed. No
ABS or Checkengine lights on when this occurs. Brake pedal gets so that
there is no travel (that's when wife knows its starting to happen again). At first, when this happens, she could pull into a parking lot, put in park, and actually reach down with her hand and give the pedal a hard jerk, that would inturn free up the wheel...I know..doesn't make sense, but she
could then finish the drive home. Then wouldn't happen for a few days, maybe a week. Finally, I test drove it and in about 2 miles I could feel the same. Got it in the garage, put in neutral and rocked car slightly to feel and hear the caliper binding. Now read this...when I opened the bleeder on the caliper it freed up instantly. I have to mention my order of replacement is out of whack. When the caliper freed up by opening the bleeder, thats when I replaced the rubber brake line, which of course didn't fix it. I am now leaning towards the HCU. Typically if a booster is a problem it affects all the brakes. Master cylinder usually affects all, or, both front or both rear and not just one wheel.
Right now I am tracing RF wheel abs sensor wires from the wheel, through the harness to the HCU. Why you ask...looks like the new battery that was replaced about a year ago has been spilling acid all down the sides. I noticed this a couple of months ago when changing the oil. Guess where most of the harnesses are located..yup, right below the battery. None of the acid hit the HCU and looks clean. The harnesses though look like hell. Soooo...once I make sure that the wires are intact I will proceed into looking into the HCU. Questions- Is there an aftermarket ABS scanner available, other than SnapOn, MAC Tools etc? and, are there codes that relate to the HCU?
Final note: I did remove the ABS fuse under the dash and it took a week before it did it again...so, nix that.
Background, I was a GM Tech for about 30 years, left about 12 years ago.
Thanks.

http://www.amazon.com/ search equus 3160
http://www.alldata.com/ sells a years service for appx. $29.95 they have good information. Make sure you copy the electrical diagrams before it expires.

Thanks randwor..will check into that.

Update: Finished tracing the wires for ABS from sensor all the way to HCU and there is no sign of corrosion from the battery. FYI, the wires from the RF wheel sensor are in the wiring harness that runs along the front of the radiator support. Had to pull both headlight assemblies to be able to trace all the way to the HCU. That harness then ties into 2 main harnesses that come together underneath the fuse/relay box and that is the area where I was concerned about corrosion. Now, halfway through this project I started thinking that maybe I should have pulled the fuses or relays that power the HCU and do a road test, too late now. I had only pulled the fuse inside the car that powers up the ABS Module. Time to reassemble and I'll do the other test tomorrow.

UPDATE, Sunday,
Car all back together, road tested with all fuses out, dash fusepanel and
power distribution fuses. Road test about 1.5miles, came back into the garage, set in neutral and car still running, walked around to rf wheel, and when trying to rock the car back and forth, you can hear and feel that the caliper is binding, almost locked. Walked back around to the car, reached in and grabbed the brake pedal and gave it a quick jab...Tada...rf releases...?????Did roadtest second time...saaaame thing. I wonder if jabbing the brake pedal is moving a valve inside the HCU?
Anyone any other thoughts?

As the power fuse was pulled I doubt a solenoid valve is moving. When it happens crack the fitting at the master cylinder does this release the pressure at the wheel.
Is their any binding on the brake pedal it seems strange pulling up on it releases the pressure. I would look at a weak spring on the master cylinder.
http://www.modulemaster.com/ They sell rebuilt units you could call and ask for guidance.

It's a quick jab down on the brake pedal, not a pull. I would have thought if it a weak spring, both or all brakes would have a problem and not just one. I checked out that site, good info, and or course the ford Ate module is not a rebuildabel unit. I need to find a hydralic schematic of the HCU, that would clear up things and make for better diagnostics. I am going to pressure bleed the system and flush out. If the valves are anything like valves in a tranny valvebody, I have seen valves stick do to the crap that resides in the reliefs in valves. I'll do that Tuesday. Before I do that though I will trace the brake line to the hcu and crack that open and see if the wheel frees up.

Update-5-14-09
Weds night flushed all brakes, ran a quart of new brake fluid through the system. Roadtest...so far so good. Fluid that came out was dirty, but I've seen worst. I'll give it a week to see if it acts up again....maybe?
Did some parts searching, looks like Focus is the only model that considers the abs module and HCU as one unit, has to be replaced as one and very expensive. If it
comes to that, I will remove the old one and see how much of it I can disassemble and possibly clean.