Now you guys have me concerned about my steel washers with rubber on the bottom I use for my air cleaners.
For a time I used Revmaster C-Channel valve covers but a couple of times I cut through the gasket when tightening them. They are now in the box of stuff to give away at Carlisle.
Now I am using CSP bolt-on valve covers. They can be used with an o-ring or a conventional gasket. Currently, I am using silicone gaskets with them.
I used to have a set of valve covers like Danny. I can't remember why I stopped using them.