I did a disc swap on my 14 Bolt FF about 3 months ago and it seemed to be working out fine for a while. The new rotors and pads were beginning to seat and wear in fine with no noise. I got an adjustable proportioning valve and got it set up to work the way I wanted. Then at one point I took a peek under the truck and there was fluid spattered over both of the tires. At first I thought it was gear oil from leaking hub seals but I took off one caliper and it's definatly comming out of it. I used the El Dorado calipers from a bone yard and they were full of fluid when pulled. The fluid isn't gushing out on the ground but when I press on the yellow rubber center of the piston it starts leaking out. OK so I need new calipers or a rebuild kit for them. Now for the second issue. While placing the caliper aside I nudged the rotor and hub assembly and then noticed I was able to move it back and forth. The hub nut must have came loose or was never tight enough. The nut torqued to spec didn't do the trick so is there a better way of getting it tight enough? Also can someone tell me why there would be a cap in the middle of a brake piston?