I rebuilt my ap5200 calipers, got all new parts from parts box, I replaced all the seals pistons and bleed nipples,
They where really easy to rebuild, I didn't undo the main fixing bolts as I read once they are apart they never seal up again
After I stripped them all down I soaked them in a tub of thinners for a few days and they came out like new and ready for paint

The cost of the parts wasn't too bad and they where really easy to rebuild