I have just got my 1970 stock 850 back on the road with some help from this forum. It had a leaking front brake cylinder and was parked up for nearly 20 years. One brake shoe was well soaked and I tried cleaning with meths, sand paper etc but the car pulled slightly under braking I ordered some new shoes but while waiting I gave them a good go over again but this time with a round wire brush attached to my drill. They came up looking new with no sign of oil/fluid stains so I refitted.
After several weeks of driving and usage they still pull up straight as a die.