When went through my 77D, the crankshaft seal behind the rotor had been leaking badly and the stator was absolutely soaked with oil.
I pulled it of and put it in a pan with kerosene and cleaned it with a paint brush, it did a good job of removing the oil. I then washed it in hot soapy water to remove the kerosene. After rinsing , I blew it out with compressed air and then set it out in the sun to fully dry. It has worked perfectly since then.