In early 2006 I laid stick-um tiles in my bathroom. I laid them on new 1/4-inch plywood. Now they are coming up (the glue gave out) and some are turning yellow so it's time to replace them with more stick-ums. What is the best product to use to remove all traces of old glue from the plywood? And, isn't 13 years a bit early for the glue to give out and for the tiles to turn yellow?