Tube amp - tube socket problem

Hi fellow tube amp owners. Four months back I bought a used Primaluna Prologue 2 which I really enjoy listening to. I'm the 3rd owner and it was built in 2004. I have a problem with one of the preamp tube sockets. One day I was very lightly dusting the top while it was running. I barely touched the tubes, and I heard a loud pop/crackling noise. Turns out the left side 12ax7 socket is the culprit. In normal operation it's fine, no noise no problems. If I gently wiggle the tube it makes the noise. It then has to be returned to a precise position to return to normal. 

I contacted a local tech who said the sockets can become loose over time and/or get some contamination from the tube pins lodged down in there. He didn't seem too keen on working on it, but said he could try to clean it out. I wondered if there was a bad ground or short, so I opened it up and inspected all the solder joints involved with that socket and found nothing wrong. I don't really want to ship it to have it fixed if I can avoid it.  My main concern is that it could get worse overtime or lose some performance on that channel from not making good contact.

Any ideas? Has anyone had a similar issue? Thanks.