i would doubt retorquing the bolts would fix the issue if that is the cause. i had a Nissan Patrol leak oil from between the head and block, cause was snapped head bolt from whoever the spastic was before me who messed with the head.
you don't have to drain the oil to take the cam covers off, the oil lives in the sump, unless you filled the engine up with 20 liters of oil.
i would go berserk with degreaser and an inspection camera and figure out exactly where the leak is. no way would a head come off unless i was 100%sure that is the issue.