I have not broken off any oil feed lines, so I think you should be okay. Patience is your friend here and so is plenty of penetrating oil and give it time to penetrate and possible reapply. You should be able to do it in car, but it may require some contortion of your body to get into the space. Ensure you use teflon tape on the threads to feed the oil or else you will have leaks (been there done that). I can't visualize exactly the oil feed line, but it may be easier to cut the oil feed line as close to the flare nut as possible and get a closed end wrench on it to get it to break loose, although with a good flare wrench you may get it off without having to cut the line. I just find that sometimes the flare nut gets rusted to the tubing and basically you end up bending/breaking the line off trying to unscrew the flare nut (very common with rusty brake lines)