I've never had a problem with champion plugs(so far)
When L10S were obsolete I used the L82C and still do in my C11's
Now the N8 is obsolete I will see how a N5C works on my alloy head C10.
I have not had use for a L10 which is now the L86C until I got the 45 C10 with an iron head (still on old champion plug)