Hiya Paul
Try swapping the thermal fuse from the old motor and rub a thin layer of fairy liquid around the rubber casing to aid shoving it into the motor bucket. If that doesn't work, move the rubber bit around the drive shaft a notch. Sometimes the connectors fit better if you push them in rotated 180 degrees. Also, if the motor has shat it's self, change the post motor filter as you will never get rid of the stink.
H