Thought I'd send a link to the only likely place you'll find a tank gasket for that saw these days. I know you can make them but, I sell everything for their carburetors, and and you can select the fuel tank gasket for the thrifty if you need that.
www.oldsawshop.com
McCulloch Model 33B, Super 33, Model 39, Mac 35 and Mac 35A 6 Gasket and carb Kit combo
New kit for McCulloch Model 33B, Super 33, Model 39, MAC 35, and MAC 35A saws. This kit contains new diaphragms and gaskets for a rebuild of the fuel system of your 3X and super 3X series saws. See list below for items included in kit. Part Name Quantity OEM Part# Fuel pump Diaphragm 1 65573...
www.oldsawshop.com