I've had good success pushing the pistons out (after removing the pads) and giving them a blast with some spray lube (I use weldtite TF2) pushing them back in and cycling them a couple of times, then clean up with isopropyl/brake cleaner and reinstall pads. Job done
I'd do that, then check the bleed.
(This is my "quick fix" technique I use at work on a daily basis, I have only found a handful of brakes it hasn't sorted: and they were found to be beyond repair)