Thanks for this post! Extremely helpful for me, as a new Supra owner. Went to purchase mine, went to pull a plug as part of my inspection and found the wire saturated with oil along with the entire trough between the 2 valve covers.
Thought it was the valve cover gaskets, but them found this post. Ordered the stock #3 cyl cover from my local toyota dealership (prefer to keep it stock) and no oil since! Fabulous.
I also got the drain plug gaskets from Napa, as the OP had recommended, but decided to stick with the OE gasket, because I preferred the material for this application (rubber with the aluminum washer, vs the fibrous material of the red gasket that the OP described) and figured that perhaps the extra support around the plug wires helped something?!?!?!? Those Toyota engineers put it there for a reason? Who knows. Anyways, doing great now. Thanks.