Leakage from where the accelerator pump shaft goes through the bottom of the carb is not something that can be stopped completely as there is no seal involved. Keeping the float level and fuel pressure in check are all you can do. It shouldn't be running out, but will develop a "film" over the parts in that area over time. Nature of the beast, sorry.
As for a warped air horn, filing or whatever will end up removing the "bead" that runs around the edge for sealing. If the carb is truely warped, toss it and fing one that isn't. Most are fine, I have yet to find one that is warped, personnally. Just make sure it is for a 216, as the 216,235 & 261 all used this carb and the throttle bores are all different, and the 216 has a smaller bolt pattern as well. You would want to look for one witha 1 1/2" bore and approx. 2 3/4" bolt pattern.
