brake line flare nut not coming off
 

trying to remove a brake line flare nut (tube fitting) that is very stubborn. the one at the top near the strut. this is the nut you untighten that goes into the soft brake line coupling that holds the hard brake line end in. have it about 1/2 unscrewed but the remaining is not wanting to turn without giving it a good amount of force. lubricated and turned it slowly over the last 24 hrs but still difficult to turn. will this mess up the threads if I put some force on it to finish turning it out of the soft brake line coupling?

Here is a pic of the nut. I decided to slowly work it out and it is almost to the point where it should come out - but it keeps spinning when I turn it and does not come fully out. I don't know if it was put in wrong to begin with or if there may be some internal rust or something keeping it in. What would be the best way to get this out fully? Would heating it with a heat gun help at all? I am trying not to screw up the nut because I have to reuse it and don't want to replace any hard lines. Any advice appreciated...

Attachment 8176

Here is an update just in case anyone runs into the same problem. What appears to have happened is that the flare (flange) nut was pressed in too hard and expanded at the top - making it hard to remove at the very end. I spent 2 hours and a couple of trips to the auto parts store with videos to figure it out. The nut almost seems like it was installed incorrectly when originally installed because it did not thread back in easily. The brake line on the other side came off super easy so this was definitely not usual. There is a 50/50 chance that his may leak because it threaded back in with difficulty - but the alternative was to relplace the whole steel brake line back to the master cylinder which I do not want to do. I STRONGLY suggest that if you have an older car - to check your brake lines. You don't know panic until you press on the brake pedal and it goes to the floor and you have no brakes...