Wouldn't leaking gas evaporate?? This is a constant build up around the base of the carb and some of the linkage. I have no idea which is that throttle shaft...
If this residue is dark brownish in color, it is probably gasoline residue after the main components of the gas evaporate. The throttle shaft is what turns when the throttle is pushed, and goes through the base of the carb.
Your carb is probably a Holley model 1945; you can find a manual here to see how things go togehter and what parts are named what; the 1945 section starts on page 20. (This is a 86 meg, slow download.) 1945 is the general model number; you need to find what Holley calls the list number on the carb before you get parts for it; that is usually a 4 digit number and maybe a letter (but could be more numbers). I'll recommend the Mike's Carburetor site; they make it preatty easy and are in WA state, not too far from you.