just came up with a piss easy way to get your astra g bonded knob off.
oil filter wrench (the canvas strap ) type
small piece of push bike innertube
cut a section out of the innertube so you have a tube about 2 inch's long, slip the tube over the gearknob this will stop the oil filter wrench from slipping. next rap the oil filter wrench around the knob attach the socket wrench and twist. with no effort at all the knob will come off undamaged (good if you ever want to put it back on) now fit nice new shiny knob (mine didnt fit, the lift up reverse bit was to big). this method works a treat no mess no fuss took me less than a minute to get the knob off. hope this helps.