agree with rojo.
IPA is good. I keep a spray can of brake cleaner around. just fucking drown 'em ever once in a while when they're acting funny. this includes removing the pads and giving them a VERY light pump to expose the pistons. have to be careful not to over-pump the brake when doing this or you'll fuck up the diaphragms and not be able to get them back in. spray and maybe touch up with qtips to get all the gunk off so they move smoothly.
I use an old butter knife to press them back in, one at a time. said knife has some flex to it so is fairly gentle on the piston. if you have a thin piece of wood like a paint stick, that could work, assuming you can get it in there.
however you do it, cleaning the pistons and making sure they actuate evenly is first thing I do.
when examining the pads, make sure you're not seeing the pins that hold the braking material to the backing plate. best way to tell how much life you have left is compare side-by-side with a new pad. if your halfway down, it's probably time. the pins will start to get exposed and will mess up your rotor.
check your rotors for warpage (not sure if you did this, above). usually, gentle thumb pressure is enough to bend the warp out. don't worry so much about if it's centered, at this point. getting it unwarped is most important.
when reinstalling a brake caliper, or just adjusting it after the pistons and rotor are good, just be extremely methodical: with loose mounting bolts, after a few pumps to make sure it's moving, tight squeeze on the brake lever, tighten the bolts in tiny, alternating increments so they are both even. if you tighten too fast, you'll torque the caliper out of alignment. that right there will cause a lot of vibration and squealing. at least as much as dirty pads.
had a pretty crappy ride today. just uncomfortable and not in control. fucking up things I never have before.
I did see this, short cutting up to session a feature. seems like there's a story, here. circle of life, etc.