Another option is Permatex "Right Stuff". It is more urethane based instead of silicone and dries quicker,and is much more forgiving if the surfaces aren't spotlessly clean. It will also form a reliable seal up to 1/2". Try that with silicone. We regasket stuff all day long here,and sometimes silicones will leak,never had a problem with the Right Stuff. Comes in both a "string cheese" type tube or a regular caulking tube.