The reserve stopped working on my petcock so I decided to replace it. I got an OEM valve and everything looks identical. When I put it on, it was slightly loose but I figured it was seated against the O ring anyway. But when I put a little gas in it, it started leaking pretty badly.

Did I miss a part or what? I put the O ring down over the filter and tightened it as comfortable as I felt tightening it before I thought I was going to strip something.