My favorite way when I start all over again is to remove the studs and "clean the deck" off on a lapping table. Most people dont have one (I dont) so about any piece of plate glass(drill press tables or even the table on a table saw work well too) and some very fine emery or crocus cloth works fine too. Yours doesnt look that bad, and when I have to reuse a metal gasket I use some sealer. my favorite is straight aluminum paint. there are plenty of head sealants that us that or copper in a shellac like vehicle to spread. Neither does much for compression leaks but it will help hold steam and water. Cleans off pretty easily too.