I would get some brake cleaner and rinse off that wd-40 let it dry while you go to the store and get some pb blaster it's in the yellow and white can. put it on, let is sit for an hour, put some more on, then lightly tap with a hammer, put the wrench on and "pop" the wrench... if the wrenching has already damaged the nut, you may require locking pliers to get it off.
John

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I second that. Try vsetch's method and see what happens.

__________________

I also agree. Any time I have to loosen stainless fastners whether it be brake lines or stainless bolts, I hit the wrench with a closed fist or palm of my hand. Never just pull on the wrench like we've all done on another type of bolt or nut. Stainless tends to lock together not sieze like other fastners. I've been doing this for years and I guess never thought to pass it on.

__________________
81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

I agree with John's assessment. WD-40 won't do anything. You need PB Blaster or Kroil for that job.

I also use a bit of heat from a propane torch to loosen things up a bit........but.........you'll need to be careful and have a small flame directed right on the nut.

Anytime I'm working on old brake lines or bleeder valves I squirt the solvent on there. Then heat it with a small torch and then squirt it again. I always have a wet rag handy if the solvent catches of fire. If the cars ever been driven in the salt I do this before ever touching them with a wrench. If the nut is already messed up on the brake line you may have to use a pair of vice-grips. Make sure you clamp them as tight as possibly you can. What sucks is when the metal line and its nut turn together. You stuck with bending in a new line then. I use anti-sieze during assembly and I also spray rubberized undercoating after assembly where the metal line meets the end of the new rubber line. It just keeps the water and salt from rusting them together again.

Just last week I put new pads and rubber lines on the 240 using this method. This car is a rust bucket but I didnt have any problems.

__________________
a few mb diesels

You can also cut the rubber hose off near the ends and get a socket or a box end wrench on it to maybe put a little more oomph on it.

Len

The problem is rarely the fitting on the brake hose. It's always the smaller tubing nut on the brake line.

and if that fails, get a Dremel and sacrifice the rubber hose metal end, just like the oil cooler lines on a OM617, but I don't see how a little heat and repeated soakings with PB Blaster can't set them free.

PB Blaster is amazing, the local NAPA sells it in gallon cans to the farmers. It also has a unique smell, sort of like airplane glue.