PRS-350 PRS350 Fell in Water, All Works, but 1 Issue

My Prs-350 fell into lake water this summer. A hairdryer/rice treatment helped dry the device, and, to my surprise, it "works"! The only issue is it developed a small quirk: the five physical buttons do not function unless pressed simultaneously with the power switch. For instance, to bring up OPTIONS during book reading I have to press OPTIONS button while briefly sliding the POWER switch, which puts Reader in sleep mode; next sliding Power switch reveals the OPTIONS menu. This applies to all five buttons. A little annoying, but I can live with it, considering I was convinced the reader could not be resurrected.

Question: Is there a way to restore the original functionality to the buttons (without the need to use the power switch)?

I've done soft resets, hard resets, and installed PRS+, but the issue persists.

Thank you.