2000 Honda Accord – Front Caliper Gremlin

2000 Honda Accord v6
150k miles

I’m frustrated by a real gremlin in both front calipers: Sluggish retraction.

Test procedure:
I have the front of the off the ground with engine running; the wheels spin in gear or neutral. After I press the brakes, say 20 times, the calipers won’t release–wheel won’t turn in gear and it’s impossible to turn by. Calipers eventually release after an hour or so; otherwise I release them by cracking the bleeder valves.

I have done the following yet the problem persists.
– Replaced internal seals and boots on both calipers. Caliper bores are pristine. Pistons are pristine.
– Replaced both bleeder valves.
– Replaced both brake hoses with Geniuine Honda; replaced all crush washers; replaced banjo bolts.
– Replaced caliper pins and boots; repacked with Permatex 24125
– Replaced pads and clips; lubed with Permatex 24125.
– Completely flushed brake fluid and replaced with fresh.

Given that the calipers stop the car perfectly but don’t release pressure when the brake petal retracts seems to indicate a check valve behaviour somewhere in the line. Old brake hoses are notorious for being the source of this sort of problem, as are a couple other items in my list. But I’ve replaced all the usual suspects with no success.

What am I missing?
Anyone else have experience with this specific gremlin and its remedy?