Microphone does not work except when on speaker phone

So to start out, this issue came out of the blue. The phone was not dropped or came into contact with water to cause the issue. However over the year and a half I've had the phone, it was dropped twice. This may be a crucial point to my suspicions on a loose solder joint or electrical short somewhere that I will explain later.

Now this may not be as simple as you think at first. As you might already know. Calls work on speaker phone because the device uses the secondary microphone located at the top of the phone.

I've followed other advice that I've found on iFixit which appears to be the 90 percent solution. That is replacing the dock connector which has main microphone attached.

If I'm not on speaker, no one can hear my voice

And the installation instructions for the dock connector.

iPhone 4 Dock Connector Replacement

Replacing the new part had no effect initially. I am testing the audio using the Memo app. So I thought it could be a couple issues. I had received the new part DOA, there was dirt clogging the microphone rubber boot housing, there is an electrical short somewhere, or a loose solder joint.

So I began first by leaving the rubber boot housing off the microphone and not replacing the back cover of the phone, speaking directly into the mic. No luck with either dock connector parts.

Then thinking it could be a short, or loose solder joint. I began re-seating the dock connectors multiple times. Eventually with the new part everything was working fine. However since I was re-seating the parts multiple times I was only reassembling the necessary steps. So when I followed all the steps, the phone no longer worked. That would be the first and last time the phone's microphone worked with either dock connector.

I was suspicious that maybe the speaker enclosure was a problem. I have access to another broken iphone 4, that may have a logic board issue. So I replaced that phone's speaker assembly with mine. No luck.

I've since ordered another dock connector part to be very certain that the part is not DOA or flaky. But because I was able to get it working that one time, makes me think that either another part is failing, there is a bad solder joint, or an electrical short. Does anyone have any suggestions of what step I should take next. I am unaware of all the components that are crucial to the microphone working, or where there may be common shorts/loose solder joints? Keep in mind, I've also not followed the steps of degreasing the suggested parts. Is it possible finger oils are preventing this?

Since all this work, I have noticed my phone sometimes cannot connect to the network unless i reboot the phone, and now my home button has stopped working. I assume I damaged the home button ribbon cable from re-seating so often. These problems I mention only in case they provide relevant information to the mic problem and am not looking for their solutions in this thread. I want to narrow down the mic problem first.

Anyways, hope the community has the answers.