I have used Vice=grips with the double flat jaws and a propane torch penetrating oil on brake lines but only when I am replacing the hoses.

The only tube I replaced was the shortest Brake tubing in the Rear as it had rusted through.

The vise grip company makes a vise grip type wrench that grabs hex nuts without rounding them. Works perfectly because I had the same problem. I don't even bother with flare wrenches unless I have to. I do not know the tool # however but they are terrific.

Those vice grips have been mentioned several times. Used on hard line if an 11mm flare doesn't work.

The vice-grip is a Irwin 4Lw and is quite small (about 4" long)

More in previous post: http://www.peachparts.com/shopforum/3340948-post9.html

I iive in the rustbelt so often have to use very high heat to loosen those fittings. Being ox/acc I never thought things got this bad in California.

I bought my Mercedes in CA but it spent time in Missouri and possibly some other states. It has rust.

Also CA has a lot of coast line and Northern CA is somewhat like the East Coast northern States as far as snow goes. It is just not as populated.

https://static.grainger.com/rp/s/is/...536&$adapimg$=

I have these and its older model too. (12 inch length)

No flare, pipe fitting or even a rounded nut has won a battle against these. Arrange them properly on the fitting, grab them tight - give a quick and heavy action.

flare nut wrenches dont hold a candle to these.

I just want to know if the OP ever got the damn thing busted loose........

Vice grips and brake union
 

I had a similar problem with a w111 brake line. After trying everything discussed above, I bought the notchy Irwin vice grips ( I had to wait for them to come from the USA -I am in Australia). The union was still too tight for them I wound up cutting through the union with a hacksaw blade stub in a holder, then filing the union down to the clip, which then lifted off. It all took many hours. A local brake and clutch place made up a new pipe using fittings from a wrecker, using steel pipe and I patiently bent it to fit. Again- hours! Good luck

No such luck! Had to take a grinder to it. I have a straight brake line of the "correct length" on order from Pelican, genuine Mercedes, and a local mechanic will bend it to shape with the right tools. I could do it myself, and I might. I just did not want to have to buy tools for a job I will do once. I have too many tools these days. Can't even find ones I know I have.....somewhere......

It turns out EZ-Fit has supply problems in the COVID era and cannot send me premade lengths of brake line right now. I read on the internet that I can bend the Mercedes steel lines by hand. I don't know, I have never tried it.

Did you not try the Cupro-Nickel pre-made lines? I changed the rear lines both sides of my 85 W123 and was able to buy those lines with Euro fittings at several parts stores in our relatively small town. They can easily be bent by hand. They come in a variety of fixed lengths.

I was not aware that generic car parts stores still carried these items. I have AutoZone and Napa to choose from. Neither sold premade brake lines with euro end fittings. I have ordered a straight line from Mercedes thru Pelican Parts and will trying bending that by hand.

I had my local Mercedes guru make a line from NiCopp, but his end flare is not working. I will have to try my luck with the Mercedes part.

I have not looked at Harbor Freight for a long time but they used to sell a tubing bender and it was no expensive.
If you have a vice you can get a long 1/2 inch extension grip it lengthwise in the length of the vice jaws and put a socket on the end that matches the radius of the bend and use the socket as a mandrel so you won't kink the line.

I thought I should finish up with this thread. I purchased a genuine Mercedes steel brake line from Pelican parts that came in the correct length, but as a straight tube and not bent to shape. It turned out that the Mercedes steel brake line was very easy to bend to the correct shape by hand. I installed this brake line and have about 3000 miles on it with no issues.