Power Steering Union Leak

Hi,
I have recently replaced the PS pump on the 172 and I cannot get the union on the high pressure pipe that goes into the pump to seal.
Is there something obvious I'm missing like I just need a new O ring or there should be 2 instead of 1?

This is the union I'm talking about:

Thanks in advance.

I found mine a real pain too, I ended up very gently manipulating the pipe end to get it to fit right

Put a new seal on it and a very small thin amount of PTFE tape on the thread . Make sure it's absolutely 100% clean and dry , tighten it up and bobs your uncle hopefully. If it still leaks then it'll be the pipe that fooked

I think mine is leaking from here ( could i get away without getting a new part and just tighten it up and use some of the ptfe tape sorry if im highjacking the thread