Thank you all for your fine suggestions, but I took the easy way out. First of all I used Form A Gasket #2 on the elbow to carb threads. The hairline crack was not visable anymore, but I knew about where it was. I made up a small batch of JB weld and put a thin layer on top of the carb and let everything set for a couple days. Today I got brave , put a half gallon of gas in it, fired it up and no leaks. I don't forsee any in the future as all the stuff I used is ok with gas.
Thanks again for all your suggestions,
Know Your Cub, And Your Cub Will Know You.