That left grip is really the only problem, right? Used to be so easy, way back when, on bikes. You could use a water hose or an air hose.
Need to loosen the glue - but don't know what kind it is....
Don't want to cut it off - want to keep the grip....
Probably need to use some heat to loosen the glue - can't use acetylene, I suppose...
Just an off the cuff idea. Take the bar completely off the bike. Go in kitchen and ask spouse for a good old crab pot. Fill pot with water. Heat water to a boil.
Put on the spouse's favorite kitchen mitt, and insert bar end into water for just a few seconds. Remove and try to turn grip loose. If it doesn't come off, try it again fo a little longer. Just watch that the rubber parts don't get deformed or something while twisting.
If it doesn't work, pick up some crabs on the way back from the bike shop