I made two big mistakes when i resealed one. First, I didn't wear gloves. Silicone burns skin. Second, I was resealing a 55g tank which is 21" tall. Kind of hard to work without sticking your head right at the top of it. I had a major headache when I got done.
Don't forget that you need to remove all the silicone from the joint you're re-sealing. It won't stick well to existing silicone. A piece of relatively hard plastic square, with one corner rounded off makes a great tool to get a consistent bead.
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