Hy cameo1956, a lot of the older buses I worked on used that solenoid, there was a cork gasket the same shape as the solenoid flange, but no seal, only the one around the shaft that it sounds like you have already removed. Every solenoid has two windings, a pull in winding (high amp draw), and a hold in winding (low amp draw). Once the pull in winding pulls the shaft into place a connection to the hold in winding is made and the connection to the pull in winding is opened. If the hold in winding is open or shorted, you will get the symptom you describe, a chattering sound from the solenoid, hope that helps.
