That big o-ring in the filter is easily mangled (took a few minutes to choose that word). Might be worth checking if urs is sucking air. Also, the relief screw at the top, check around there too.
Also, I used tape on all connections. Might help
I've pulled it apart a little while back as I was swapping it to a different keg. The seal looked ok. I have now done up all the fittings super tight, thought I was going to break something. I've got heaps of thread tape on everything, so far so good. Thinking now I should have put some seal lube on the seals to help prevent it bunching up when locking it up.
QldKev