I'd shop on ebay and try for GM or Victor old stock vs something made in China. Langdon's Stovebolt should carry the crank seal or Patrick's in Casa Grande, AZ and Chevys of the 40's. These guys should be linked to this site or check the vendors over on Stovebolt.com.
Best of luck
Jim

Jim, I.I. #173
(It's easier to get forgiveness than permission!)