Volume Problem after water damage

I purchased an iPhone 4S with a red humidity sticker inside of the earphone jack - signifying possible water damage.

Problem: Upon a thorough checkup I noticed that when the volume buttons were pressed up/down, the speaker symbol would show up but the bars under it would not move - as in that the volume was not changing. The volume through the speakers did work on apps like Youtube but for things like screen lock and keyboard sounds it would not.

My troubleshooting so far:

• Switched the motherboard to another working iPhone 4S frame and problem persists.
• iPhone is not on vibrate.
• Clean restore through iTunes (no backup)
• Hard reset (power and home button)
• Played around with it on the dock, it fixed the problem momentarily for about 2 seconds, then it came back.
• Cleaned the charging dock with a toothpick and then with alcohol.