scribe a line across where the rear cover/cam case/front section join ,undo the bolts holding them together,when you split them make sure that the vane inside does not come off the rotor,the o rings in the cam case should be replaced,the snap ring on the end of the shaft needs to come out,then pull the shaft out and replace the cam case and rear cover to stop the vane and rotor falling out,then flip the unit over and you can remove the offending seal........the other possibility if you can stop the pully turning is to undo the pully nut and get a puller on the pully then when you have it off prise out the seal