Touch screen erratic after minor water damage?

I have an iPhone 4 CDMA which suffered some minor water damage. The touch screen is sometimes erratic and "works by itself" eg opens apps, dials the phone, zooms in and out in maps by itself.

Removed logic board and inspected all the visible solder joints with the microscope and I cannot find ANY corrosion. The board is VERY CLEAN almost looks in factory-fresh condition. Already performed several IPA scrub-downs and tried the board in a completely different, known-working body (EVERY part different, including screen and battery). Has anybody else encountered this issue? Could you point me in the right direction on where to inspect the logic board's digitizer circuitry? I do not have a schematic for the CDMA board.

I am a hardware tech and am capable of performing SMD, BGA and reflow soldering.

Thank you in advance!!