You will need to put on your Tin Smith hat to do this right the first time.
First you need to flatten the screw holes and straight obvious bent sections.
Then screw the cover on without the gasket and use a thin feeler gauge between the screws to find areas which need more massaging.
If you get this done, you won't need fancy sealants. A thin layer of Permatex #2 will seal it up nicely, and it will be easy enough to remove the cover the next time it needs to come off.
