Definetly what the above poster said. Except I would do both sides to be safe, but obviously not needed.
Just a quick question though:
How did you know you have leak, specifically from the valve cover gasket?
I'm asking because when my VC gaskets and tube seals leaked it was ALL internal. There was no visible oil loss, or dripping from the motor. The only way I found out is because of a misfire, and I checked the plug boots finding them covered in oil.