Can't help you about the noise, but...
If the rear lever feels squishy, then it sounds to me that you've got air in the line. That may be the sole reason for the lack of power back there too, not contamination. Although I suppose it's possible you have a bum seal on one of the rear pistons (which let in air), and oil has leaked out onto the rotor and pads. If contamination is a problem, you should certainly be able to clean the rotors. I'd try taking the pads into work and soaking them in hexanes or toluene or whatever hydrocarbon solvent you've got lying around. That should remove any mineral oil (assuming it doesn't damage the pad or delaminate it
). Or you can try the blowtorch method. Personally, I'd use a bit of solvent.
If the rear lever feels squishy, then it sounds to me that you've got air in the line. That may be the sole reason for the lack of power back there too, not contamination. Although I suppose it's possible you have a bum seal on one of the rear pistons (which let in air), and oil has leaked out onto the rotor and pads. If contamination is a problem, you should certainly be able to clean the rotors. I'd try taking the pads into work and soaking them in hexanes or toluene or whatever hydrocarbon solvent you've got lying around. That should remove any mineral oil (assuming it doesn't damage the pad or delaminate it