I have an old MFJ-557 practice keyer that I picked up
for showing my son and other Scouts - morse code -

I seem to recall a general problem with the "contacts"
of cheap straight keys...
They must oxidate, corrode, or tarnish
in that the contacts are intermittent and squeaky -

Is there anything we can do to help ?
Some oil, WD40, etc to retain the electrical contact,
but reduce the tarnish & spotty sound -
Phil - WA9TKA -