To add more heat to the issue...it is heat that usually destroys the
switch/contacts.  As the clean surface area of the contact is reduced by
corrosion, spooge, mousechets (smaller than a ratchet)  the current density
(coulombs/sec-m2) increases and since the nominal resistance of the contact
surface per unit area remains the same you have more current through a
smaller patch and the power dissipated as heat at this junction rises,
heating the whole assembly, melting the plastic and smoking the mouschets.

A partial PM is to occasionally work the switch from position to position
several times with the POWER OFF.  This may help to wipe off the spooge and
increase the usable contact patch (area).

However since phlogiston theory dictates that all this electrical gadgetry
actually runs on smoke.  When the smoke finally escapes, it stops working
and you can't put the smoke back so you have to replace the part that lost
it's smoke, like that switch.  When you do you have the opportunity to
remove the extra mousechets, brown recluses, old roaches from the previous
owner and similar schmutz.

Of course nothing is as easy as it's described, nothing is a simple as it
looks, and the time to complete the task always exceeds the allotted time.
That's why you work on it yourself, to save money at the expense of wits,
knuckles, tools falling into the unknown crevices from which they cannot be
extricated and will rattle unmercifully until rust sets them free.

"Breathe in, Breathe out, Drive on"  apologies to Mr. Buffet.