I was recently servicing my forks, and at some point I must have gotten oil on my brake rotor. The performance has dropped to about 5 percent of what it used to be, and there is a slight groan at low speeds. I've cleaned my disc with methylated spirits, but that didn't do much, so I tried taking out the pads and resurfaceing them, and cleaning the disc again. Still no better. Will I need to buy new pads or a new disc, or can I perform some DIY servicing and return my brakes to their former glory? I'm running Deore XT's on 2pc 8inch rotors.