How do you tell if your valve cover is cracked?

[TerminalTalon]

I have a couple spares that I’d like to clean up and sell or just have for spares. Without installing and having crank pressure show me a crack, is there any way to verify before putting in the effort to clean them up?
I understand they usually crack around the inner spark plug plate with excessive or uneven torque but are there telltale signs?

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[chrysler kid]

Usually the under side of the bolts around the spark plug tube seals have a hairline crack under the bolt holes