I work in electronics. Coincidentally the same industry that this assembly is (Flex Circuits and Connectors). The problem is a fundamental flaw with the audio jack itself. inside it seems to use almost a ball bearing type of connection. Sure, you can push and hold it, but you may just find out that simply spinning the headphone plug will allow you to find a 'sweet spot' that will allow for listening out of both ears. This is because the ball has probably worn out in some areas and the low spots cause it to miss the connection. This is not an ideal solution but a band aid. Replacement is likely the only 'permanent fix'.