Soap and water mixture. If no go with just one that, you could try heating rubber w/a hair dryer and see if it makes the rubber. any more pliable. If still no good, put the metal part in the freezer and then try to install after metal part cold. I used to rebuild gear boxes for a machine used by an optics company with a worm gear and bearing and I would put worm gear in freezer and ‘gently’ warm bearing on a hot plate and then bearing would go on nicely. Just a thought.