Berryman B-12 Chemtool Fuel System Cleaner (part #0116) will clean up the old gum, sludge, and varnish. 0116 contains 15 fl oz, but the product is also available in 1- and 5-gallon containers as part #s 0101 and 0105. Due to the severity of your application, the process may require a few soakings. Be sure to drain or carefully syphon as much of the B-12/varnish mixture out as possible after each application. Good luck!