I have bought some new extended braided brake hoses. I though to replace then all as they have been there since new, and I will do them when I do my rotors. But the nut on the front brake line (front diff to chassis) against the chassis is well stuck and last time I tried to undo it, to replace the hose with a new rubber hose, the spanner was slipping on the nut and has started to round off the nut. So I left it at that. Now I need to attack it again. As I can see me in the end using vice grips to undo it and totally destroying the nut.

Any tips?