FWIW, I once compared a used trans/diff gasket/washer to a new one using a digital caliper and the difference was barely enough to confirm that it is a "crush" washer of sorts (though it is nothing like the oil pan drain plug copper crush washer). Not enough to worry about reusing if you don't have new ones. I'm certain I have reused one or more at least once when I mixed up the new and the used washers during a fluid change.
But considering the cost of a new washer is so minimal, I just prefer to know that its new every time. I keep a handy stock of them now and have plenty to share with local forum members if they need them as well
