Yes try ang get out all of the silicone you can. i didn't seperate the glass. I just scraped off the inside and outside seals then took a need and pushed through the bottom seal. once i was through i got some picture wire and sawed at the silicone. its a big pain but it worked. i am sure i didn't get ALL of the silicone off the glass but i did my best. one of the really expierenced guys on hear told me that silicone would stick to silicone if its very clean. i know it did in mine. just get the old stuff out the best you can and keep wiping it down with alcohol. get it as clean as you possibly can! If the tank is on its side you can see the silicone squeeze into the bottom joint as you apply it.