AU XR8II front brake caliper issue ?

[galaxy xr8]

Hi guys I have a slight issue with my XR8, the passenger side front caliper the bottom piston seems to be not releasing right, I only just flushed and changed brake fluid 2 months ago, but in saying that prior to this change the vehicle has seen very little use and I believe from this the piston may have some slight rusting which is stopping the piston from retracting as normal.

I first noticed it when I jacked the car up and the wheel would not spin freely, so upon further inspection I have since found that one of the pistons will push out under load as normal but it doesn't then retract and locks the pads against the rotor, I did a quick flush this evening and noticed the fluid from this line alone is not clear like it should be and the fluid is fresh, so I'm assuming that over time and from lack of use this piston has developed moisture and rust and has seized slightly.

Since flushing once it has free'd up a little but after a few pumps again this same piston doesn't release and with every pump it just gets harder against the rotor.

Would numerous more flushing of this line eventually clean this and free the piston or am I up for a kit to be put through ?

Anyone have any suggestions ?.

Cheers.