[psomers]

More than likely your old caulking is silicone. If you re-caulk with anything other than silicone best to remove as much old silicone as possible. Use plastic scraper and goo gone to remove. You can re-caulk with silicone over old silicone but any other caulk silicone needs to be removed as most caulks don't adhere to silicone.
There are probably better caulks out there but silicone can be found anywhere including walmart and easy to apply.