I've restored a lot of Commando valve covers over the years and suspect that your leak may be due instead to a common problem; they've been overtightened and the gasket rails are no longer flat.
Pull the offending leaker and take a look down the long sides. They're usually pretty tweaked after 45 years of loving prior owners. :-D Straighten any bent edges and flatten the mounting points as needed. These are a few of the typical issues.
Note the bulge near the bolt hole on the left valve cover ... the "Leaning Tower of Pisa" stovepipe was also mildy entertaining, as is the factory's plastic dip on the wire harness retainer.
