I have a used boat with a skeg box leak, tolerable but irritating. I plan to test for the leak location, clean the surface there, retest, then apply lexel, test again etc. It's a hard area to get at to clean, but I'll give it a shot. My concern is that it may have been repaired with silicone at some earlier time. How well does lexel adhere to silicone, if a residue remains after cleaning?