[shorod]

The fact that after sitting it will release really causes me to doubt the issue is the caliper. That's pretty typical of a failed brake hose.

When bleeding the brakes was your friend using a vacuum pump or having someone press the brake pedal? If using a pump, was there a good flow of fluid or was it more of a trickle? Pressing the pedal would force enough fluid through to easily overcome a collapsed brake hose, but a hand vacuum pump might struggle.

Trying to compress the caliper with the bleeder open will pretty quickly identify if the issue is the caliper or the hydraulic system to the caliper and might prevent you from replacing expensive calipers that are not going to fix the issue.

-Rod