Dont use silicone to seal water out. It will look good but wont hold
the water out.
The tar is a much better option and you can buy in in a tube and apply
like silicone carefully with a very small sharp cut, under the rubber
seal, when bone dry and clean. It will last years. Do it in sunshine
when the rubber will be soft.
When silicone hardens the water will get under it and become unsightly
and you will pull it out like a rubber band next year when you return
to repair it.