I have a small part holding, I think this is the part you want. Now here I am trying to give useful advice and not playing the blame game.
When you tighten these fittings, you must not have the spanner in a position where it can crush the thread, they are not steel, but Nickel plated brass. The spanner should be well fitting and below, or avoiding the threaded part, on the flat part (obviously)
A second tip, I can see PTFE tape on there, if you use the right amount it should be tightish all the way in (not so tight for the spanner to crush the thread). It’s also critical not to tighten the bejesus out of it, as when it has a sufficient quantity of PTFE on it, it won’t leak and only has to be almost tightened to the right position. That nut behind the fitting should of course be tight.
So basically I am saying you fecked this one up…only so you don’t do the same with the fitting I will send you. Not because your warranty would be affected, because the thing shouldn’t have leaked. I would just appreciate you paypal me the postage once you receive it.
Use the contact link in my sig, so send me an e-mail with your address. Or if you are near to Byfleet, Surrey you can collect it. I am assuming you are UK based of course.