Firsts of all I hope they mean valve cover or head cover gasket. One does not really want them taking the head off. Probably a precaution if they ruin one, taking the covers of. With that said I have never replace one on my ST in 90k miles. By using a bit of blue RTV, My valve cover gaskets have sealed up nicely.
Sorry, you are correct. I meant to say valve cover gasket. The first time I talked to them they said they needed to replace them. The next time I talked to them they said they would order them in case they needed to replace them. I don't think the individules I talked to really knew. I hope the mechanic does.