GRAVITY?????
How does gravity pull the oil sideways through the seal?
The ONLY way oil is getting pushed out of the valve gallery is if the pressure in the valve gallery is higher than the pressure outside the valve gallery. The valve gallery, actually the whole motor should have one bar or less of pressure inside the cases. Less is better, negative pressure is best.
Honda gave you a nice big thick soft neoprene gasket that compresses to seal the valve cover so there should be no "microscopic gaps between the gasket and mating surfaces" if you apply the recommended torque to the valve cover bolts.
So no need for silicone.
As long as the "washers" are not so flattened to allow the bolt to bottom in the hole, they weren't your problem in the short term. The purpose of those "washers" are to isolate the valve cover from the vibration of the valve train (in case you didn't notice the valve cover bolts go into the cam caps). In the long term, if those "setting rubbers" (that's what Honda calls tham) are flattened out and hard, the vibration would be transmitted from the valve train to the cover and then flatten out the big o ring and loosen that joint, causing an oil leak.
Honda does not call for any sealing compounds on that gasket, but that big "o ring" never sits flat in the groove so I use Threebond to glue it into the groove before I install it. When you remove the valve cover again, the "o ring" stays in place in the valve cover and you never have to putz with it again.
Not sure why I feel compelled to respond, but I will briefly;
I did apply the recommended torque, and in the correct sequence.
Yes, Honda gave me a thick rubber gasket.
The service manual itself calls for RTV silicone around the halfmoon cut-outs and corners.
Yes, as I stated above, the washers were flattened with age and time.
Well, I removed the gasket, because, when I removed the valve cover, it partly disconnected from the grooves.
And yes, I fixed the problem.