My 1986 Spider was missing the plug gasket when I bought it. I bought a copper gasket and promptly overtorqued it. I then turned one from brass with me old 1936 South Bend lathe. Works great after at least 10 oil changes and doesn't leak. You too can take your oil plug, or make a drawing, and take it to a competent machinist. It may cost more than the copper gasket. You do want a gasket there IMSO.