So you have a leak in the steel line?
any chance of posting a picture of it ?
There have been some discussions lately on replacing steel brake lines... did you try a search ?
Just remember that only steel can be used... and that the flare is going to have to be the same as what comes off it... which for brake lines is typically a doubled end.... not the correct nominclature... but memory isn't giving me the other one.... has to be double on brakes because they are kinda important...and that is stronger...
If you find that it is a rubber line then there is plenty of advise to be found using the search.... if you can't find what you need speak up....
Be sure to use " flare" or " line " wrenches.... to keep from warping the tightening nuts....and always use TWO... one to hold , one to tighten...