Removing tight hydraulic line from slave cylinder

[mlipmd]

Sorry if some of you on here see this as a duplicate post as I put this on the ZR-1 section of the Corvette Forum also but got no responses, so I thought I'd put it up here.
I needed to replace my clutch slave cylinder on my '90 and before tackling this job, I did a massive amount of research first on the Corvette Forum, , on ZR-1.net, other 'vette forums, YouTube, etc. I got the front of my car elevated 10" off the ground which lets me snake in from the driver's side for access. One handedly, because of no room in between the components, I managed to remove the slave cylinder but had absolutely no way to access the fitting on the hydraulic line going into the top of the slave. I thought I would get that apart after I was able to drop the slave down with the line attached. That nut is on REALLY TIGHT. I had it soaking in PBBlaster which so far has not helped. My fitting is a 13mm and regular 6 sided wrenches have failed to budge it. I have on order some metric flare nut wrenches to get a better grip on it and try and avoid rounding off the nut, but are there any other suggestions to break this loose and also not damage the line itself? Can I heat this up with a torch or a heatgun to try and loosen it? I really don't want to bugger up that fitting and then have to replace the whole hydraulic line, another major PIA taking everything apart to do that.
Maybe I should put my old slave back on the studs on the bell housing and try again, but I don't want to even think about breaking them off either.
I can't believe anyone would tighten that fitting so much but maybe it's from sitting there for between 25-33 years like that.
Any suggestions about the heat or anything else would be greatly appreciated.
Thanks.