Probably my next effort would be removing dead key to try cleaning under it.
This task turned out quite easy and rewarding. I popped up the key cap by sliding guitar pick under its side. Under the key I found white rubber(?) mat with a circular whole in it for key stem. Lifting up a corner of the mat revealed that underside of mat has a circular black ring under which there is a matching shape of shiny metal (copper?) surfaces separated in two halves. It appears that black ring is conductive and is pressed against the metal surface on key press.
I did not observe any suspicious debris on those matching surfaces, but nevertheless I wiped them with q-tip soaked in isopropyl alcohol. Then after putting the key back and turning on device I found that previously dead key register each and every press reliably.
Having done that I now would recommend against bashing intermittent keys no matter how emotionally satisfactory that would feel. Cleaning keyboard mat and contact points does seem to resolve the problem reliably. Although cleaning inner keys might require removing multiple keys caps.
