I have an old claw foot bath tub I am redoing and I am having trouble removing those stick on "flowers" that people use to keep from slipping. I have used a razor blade to remove the plastic top layer, but I am unable to remove the glue that holds them on. They have been stuck on for more than 20-30 years and are really tenacious. I have used Goo Gone and Goof Off with little success. Help!