Sledsel, What you are experiencing is old glue. When I see the entire area under the decal turning yellow, I flood the decal with water and then brush away the yellowed glue as it comes out from underneath the decal. Dip a paint brush in water and apply very generously over the decal. I have paint brushes that I only use for decal setting solutions and I use one of these brushes for this. You may have to soak the decal a few times. This will usually flush out the glue. Once you get all or as much of the glue out as you can, blot the decal dry with a paper towel. You have to take some care as you can wash out all of the glue and the decal will not stick. My experience has been by blotting the decal dry, you preserve enough of the glue under the decal so it will stick. I always clear coat a car in which this happens so there is another bonding agent for the decal.