The switch I installed on Mary’s bike a year ago was intended for indoor use only and, without any trace of weather sealing, recently became intermittent. No surprise, as it’s happened before, but, by regarding my vast assortment of little switches as consumables, we get a low-profile / tactile / E-Z push PTT button without forming a deep emotional attachment.
Anyhow, you can see the unsealed square perimeter of the switch actuator:
The light-gray button sits on a post molded into the actuator. Pry the actuator out and the switch dome shows crud worn off the cross-shaped plunger:
The underside of the dome has a weird golden discoloration that surely wasn’t original:
I have no idea how a liquid (?) could have gotten in there and done that without leaving other traces along the way. The contact bump on the discolored leg had some crud built up around it which responded well to a small screwdriver.
Contrary to what the symmetrical four-legged dome might suggest, only one leg rests on a contact in a corner:
So, yes, a bit of dirt / corrosion / mystery juice in a single spot could render the whole thing intermittent.
I removed the obvious crud from the obvious spots, wiped everything down with some Caig DeoxIT, reassembled in reverse order, and it seems to be all good again. Of course, these things only fail on the road, so it’ll take a few rides to verify the fix.
The Smell of Molten Projects in the Morning 
High humidity usually does the trick. My calculator stops working during the monsoons and is cured wiping down the contacts with Isoprophyl alcohol. During that time I find water drop on my table and everything rusting.. even water drops on the keyboard.
Probably you know that you get these switches in different operating pressures. The type that are in a mouse are low pressure and PTT ones are harder in some rigs.
You get condensation in places where we don’t even have places!
I must confess I don’t recall ever buying a switch with a pressure spec. Heck, the usual bottom-feeder suppliers regard a specification as a stretch goal. [grin]