Does anyone know of an ABS expert that could help solve my problem?

My brakes are occasionally binding but sometimes jam on solid. I have traced this to what is probably the actuator not releasing the pressure to the calipers as if I slightly undo a caliper bleed nipple, the pressure is removed and the calipers retract to free up the brake. If the brakes jam on, then afte 30 to 40 minutes with engine stopped they free up (presumably as pressure reduces).

When the brakes bind, it is noticable when, say, coming up to a junction that when you release the foot brake coming to a stop, there still seems a slight braking effect.

I do think it is some problem with the actuator.

I'm really looking for someone with a lot of detailed knowledge that could help. PM me if you want. I have a lot of diagnostic check manuals but all those check out OK so it is probably not a sensor or something.

Thanks in advance.

Richard.