Isn't the frame warranted for life? If you're not the original owner, or if it'd be too much bother to take advantage of the warranty, then I agree with cyccommute and homebrew01 - DO NOT take it to an auto shop. An arc welder could destroy the tubing before the operator knew what was happening. By then, an "oops, sorry!" won't cut it. I think brazing would be the best choice. No chance of destroying the tube, and it won't require a master welder.