I have finally started working on replacing my master cylinder and I need to replace a copper washer to insure a good seal. It is part # 90435590200. This is a 12 mm copper washer and my search on the web keeps coming up with "No Longer Available" . Is there a source that I do not know about or a substitute ? I am afraid to use the old one for my luck with reusing washers on brake lines is not good.