Are all 12 bolts the same length? If so then your best bet is to install new threads with a Heli-coil or a Time-sert replacement.

Band-aid approaches are a short term repair at best and on valve covers they are almost futile.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now