As far as the leak goes I doubt it needs a washer. Usually those type of fittings seal themselves. Try polishing both surfaces of the flare with some steel wool then clean really well. It probably has a small burr you can't see.
I tried a couple different times cleaning and finally put a very small amount of silicone sealant on the head of the fitting and the threads...so far no leak. I'm sure the polishing helped a lot as well. Everything is working now!