Woes with leaks and aeration

[Sláinte!]

I am having a problem with one of my kegs.

It is a pin lock keg; I bought it (used) near the end of last year. It was holding pressure when I bought it and I did not take it apart for several months. At that time, it was still holding pressure.

After a thorough cleaning and sanitizing I filled it with beer. Afterwards, the keg would not hold pressure. I could find no audible leaks and could not see any bubbles form when I spritzed the various sealing locations with a Star San solution. However, when I connected my gas fitting to the gas post, I could hear gas leaking from the fitting. The beer would also serve very frothy and muddy-looking (it's a dark lager) and there is definitely a lot of air coming out with the beer. You can see the bubbles in the fluid line when serving.

Tonight I replaced the poppet valves and the o-rings on the posts. Now the keg seems to be holding pressure (I'll know better after it has sat off the cylinder for a while) and I no longer hear the gas leaking when the gas fitting is connected. However, I STILL have the same aeration problem when serving. I also cannot detect a leak, either audibly or by spritzing Star San. I was serving with a picnic tap; I switched to a different picnic tap that I had been using with a different keg with no issues but I still have aeration problems. I even squirted Star San into the relief valve when the keg was on the cylinder but did not see any evidence of a leak there, either.

What should I try next? Do I need a different leak detector? I have had minor keg leaks before but nothing that caused such aeration issues.

[JMcG]

Just a guess: I'd check the out dip tube for schmutz somewhere up inside?
jim

[Rob Martin]

had to look that one up

http://www.urbandictionary.com/define.php?term=schmutz

[JMcG]

Rob, you're a mensch.
jim

[Matt]

And you're sure it's not the QD that's got a bad gasket or something?

Matt

[Sláinte!]

And you're sure it's not the QD that's got a bad gasket or something?

Matt

I tried two different quick disconnects, each with its own picnic tap attached. One of the QD-PT units was being used without issue on a different keg. The same problem manifested itself with each unit.

[Matt]

I figured as much... but wanted to rule it out.

Matt

[Rob Martin]

Rob, you're a mensch.
jim

That would make you an Übermensch

[JMcG]

Rob, you're a mensch.
jim

That would make you an Übermensch

Sie sind zu freundlich.

[Sláinte!]

I found the culprit(s). I changed out the o-ring dip tubes and now there are no more leaks. I think I was not able to get enough StarSan shot up underneath the posts and that is why I could not see any bubbles.

While I was at it, I changed the lid's o-ring, too.