If it's leaking at the mounting flange I'd pull the whole thing off, clean off the old caulk and reseal it with some butyl tape. Make sure to get the tape under the screw holes so water can't get in through them.
If it's leaking at the lid it will probably need a new gasket.
I didn't even think about the lid leaking. I will need to check just where the water is coming from. Thanks for the tip and sending in the right direction.