Use mineral oil. Do not use any DOT fluid in it, as it'll rape the seals, and pretty much everything else. I don't think Dani meant to take the brake off completely. Just had to undo the bolts (that hold the caliper on) slightly, pull the brake, and then do the bolts back up. In theory this should work, as when you pull the lever, both pads come at the same time, which should center the rotor in the caliper. - Meaning no/very little rub. Now you say it's not holding, you've probably contaminated it somehow. take the pads off, and boil them. - Wack them in a pan with some water, and put it on the hob for a while. Hopefully all the oil will come off. Another thing to try, is get a lighter, and just burn the pads a bit. Once all the black smoke has gone, that should mean you've burnt off any oil on there. For the rotor, put it in the dishwasher (obviously wash it in there) and that should be fine too. All of these has worked for my BB7, so I don't see why it shouldn't work for any other brake. Just be sure to not get any oil on the pads or rotor when you re-bleed it.