If its just the button that failed, you don't need to remove the knob as the button assembly just slides out. It's best done with a proper trim removal tool to avoid damaging the gear selector knob but if you're careful you can just use a flat bladed screwdriver. There are instructions online if you can track them down.
Mine cracked as shown here:
You can get a new button unit for about £10 but I found the early type was tricky to get so in the end I just glued mine back together. The one on left was the replacement (which didn't fit) and mine was on the right:
