not silicone .. gasoline dissolves silicone. There is no 'instant' gasket maker that is good for this application.
Yeah, the groove in the bowl's top edge is there to hold the O-ring. Get a new O-ring if you can..
Or cut a paper gasket to fit it .. buy genuine fuel-resistant gasket paper at the autoparts store for a couple bucks. use Xacto knife .. scissors.. and a leather punch to punch the small screw holes.