Best 383 valve cover gaskets to stop all the leaking

If you try to use rigid cast aluminum covers on stock heads which are often not machined, you can almost never stop the leaking. In that case use stamped sheet metal valve covers and install them like RRR showed above.
If using cast/machined covers on machined heads, well they really should never leak. I like those Moroso Perm-Align gaskets with no sealer at all.