Don't know about a wood lathe but to a metal turner the idea of putting a washer of any kind behind the chuck is a definite no no. The manufacturer will have gone to a great deal of trouble to ensure the mating surfaces are accurately machined to ensure your chuck runs true, now you are proposing to undo that by sticking a plastic washer in there. Just make sure the threads are nice and clean then just put a smear of copaslip on them, and the mating face. The chuck on a metal working lathe gets a lot more force applied to it than a wood lathe ever will, but I have Never known one seize on if you follow that method.