All flex headers start seeping the black stuff sooner or later. Just clean it good like PE said , wrap about 3-4 layers of plumbers tape around it and call it good. BUT....if it's actually broken...you could have it welded while it was on the aircraft so you don't lose your correct bend. But you have a chance of getting some of the weld inside the pipe and could cause performance issues. Worst case scenerio ......you might have to get a new header if it's broke. OR....you could get some new flex from A.I. and try to re-soder the new flex into place. Hopefully it's not broke.