Took some time cleaning up the valve cover, particularly the gasket area, which had some old silicone and gasket adhesive. Non-chlorinated brake cleaner seems to do a good job of this. Tried polishing up the valve cover with some old Mother's Aluminum and Mag Polish. I say "old" because I've had it several years and it was a little crunchy on top, but I did make some progress. Then I spilled it all over the place. Finished cleaning the cover with brake cleaner, WD-40, and carburetor cleaner. It's not super-shiny, but it'll do. I slipped the cover back on to keep bugs out of the cylinder head.