valve covers that won't leak - ??

The way that I've dealt with bent/warped holes on stock valve covers is I take a wood block, like a 2x4, and sand a radius on it that fits the top of the valve cover where the bolt goes. Then I turn the valve cover upside-down, press it over the bolt hole against the radius, and hit the hole with a ball peen hammer. This flattens and even curves the hole upward slightly. Makes it last few a few more times taking it on/off.

In addition to doing that I bet those triangle washers or longer hold-down pieces would work pretty well if needed