10% ethanol gasoline is an excellent varnish remover.
It effectively dissolves 70 years worth of varnish clinging to the inside of original gas tanks in pterry short order, causing the varnish to collect down stream into the fuel pump, carburetor and valve guides, gumming everything up.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission