Reddit reviews Max Professional 2015 Contact Cleaner (DPC) - 11 oz.

This should fix that issue in most knobs:

http://www.amazon.com/Max-Professional-2015-Contact-Cleaner/dp/B004PHDLQY?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_search_detailpage

You have to take the plastic covering off and spray it inside the knob thing on the circuit board. Should look like this: http://ecx.images-amazon.com/images/I/512sGRdBjgL.jpg. If it's covered there is usually a hole for spraying into.

It might be contact cleaner. I got this one from amazon to use on my camera's jog wheel since it was unresponsive at random times. If there's a Fry's or Micro Center nearby, I'm pretty sure they carry some in store

If he's electronically inclined I suggest checking out this link

http://rellinger.blogspot.com/2012/12/replacing-middle-button-on-logitech.html

If not willing to solder and replace the switch, get one of these

http://www.amazon.com/Max-Professional-2015-Contact-Cleaner/dp/B004PHDLQY/ref=sr_1_1?ie=UTF8&qid=1420242985&sr=8-1&keywords=electronic+contact+cleaner

And spray liberally so that it can seep in and do the job and hope for the best.

Would contact cleaner work in this instance?

https://www.amazon.com/Max-Professional-2015-Contact-Cleaner/dp/B004PHDLQY

It's probably corrosion or deposits built up on the PCB from the liquid damage causing inconsistent contact.

You can try blasting it with contact cleaner - like https://www.amazon.com/Max-Professional-2015-Contact-Cleaner/dp/B004PHDLQY

Just blast it in there, probably won't have to take it apart if the slim nozzle will reach. But make sure to hit all affected areas.

Note though that it might be corroded so badly that no amount of cleaning will help, but fingers crossed.

I'd try some electrical contact cleaner before I tried anything else.