E30 front brake calipers
 

one front caliper is not releasing fully.. binding and squealing.
70k miles up on an 1993 car, ABS and vented disks.

whats a likely casue? rusty cylinder/piston?

is it nessessary to replace both front calipers as a pair, even
though the other one works fine?

all new front disks, pads and full fluid change going in when i tackle
it.