I would suggest removing the old because the old won’t look good with the new, and as mentioned, silicone doesn’t stick the greatest to old silicone. I would make sure the glass is squeaky clean of old silicone….use a single edge razor to scrap off all the old stuff.
And John, RTV products are a silicone rubber compound that cures at room temperature….RTV stands for “room temperature vulcanized.” Live long and prosper!
HD maybe?
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