I use oil or grease on flare fittings, you want the flare nut to spin on the line, not the line to turn in the fitting. New flares are sometimes hard to get to seal, so the lubricant helps give that little extra turn. Teflon tape out on the threads only also helps lubricate if you don't want oil or grease on them.
When inspecting the fittings, look close at the taper inside the fitting where the line will seal to. If it's out of shape or crushed, you may never get it to seal. New factory made flare tubing has some crush room still in the end of the pipe, this conforms to the fitting. If the line has been overtightened, the crush to fit has been used up, so the fitting flare becomes even more important.
My local ACE carries these in the yellow plastic parts bins with all the other odd ball springs, bearings, and what not. Most NAPA should have them as well.
Joe
