Step 5: Cleaning/Prep: Use a small amount of brake parts cleaner on a clean cotton rag over the entire piston cylinder area, this may take a while, be meticulous. Do not use anything abrasive. Your pistons should look like this if they are not scarred or damaged. To further clean the pistons, use steel wool #0000 for surface rust or to polish them up. Before re-installation clean the pistons with some compressed air to remove any particulates.
The cylinders cleaned are shown below as well:
Step 6: Assembly: Coat the entire piston just below the outer rubber dust cover with red rubber grease (can be found on Ebay) to ease the re-installation of the pistons into the bores. At this time stretch the inner rubber piston seals over the pistons and seat them in the recessed channel.
Step 7: Install the rubber outer dust covers: Carefully stretch the new dust cover into the pistons outer recessed channel (make sure it is seated properly). The piston on the left is the correct way to set them up back into the caliper housing. The right piston in this pic is an illustration just showing that the dust cover is correctly installed and seated. Once all are seated on all 4 pistons, it's recommended you pack the inner portion of the seals with more red rubber grease. This will ensure a water-free/contaminate free environment once you place the pistons back into the calipers and seat the dust covers. (This grease is not shown in the pics)