So, what's the word?

When I was coming up we used gasket sealant on any two parts that were being mated with a cork, felt, or just about any other material (except metal with raised crush zones) in between - unless it had an O-Ring.

Now I read here and other places that some people do not use sealant on valve cover gaskets. And even in DIY threads for water pumps, valley pans, and other parts I see very little mention - if any on the subject.

So, what is your rule of thumb as to when to / not to use gasket seal?

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2006 X5 Sport 4.4i