Fingers crossed this new gasket works well and I don't have to look at ditching my aluminum cover any time soon! The other factor I noted was that there's a big steel hook at the back of the engine attached via two cylinder head bolts. I presume it's for pulling the engine out. However, that big hook sits slightly in the way of the valve cover, causing it and the gasket to overhang the mating surface on the cylinder head by about 1/16". This also seemed like a possible reason for the leak, since it was only leaking on the side with the overhang. I was tempted to loosen the bolts and try to adjust the placement of the hook to correct the clearance, but didn't want to get into breaking loose and then re-torquing the cylinder head. Wasn't sure what regrets I would have afterward. The gasket was cheap and not hard to replace, so I figured I'd swap it out as planned and see how it goes!