Obviously you 'feel' a grungy contact is not good. It's
called being an old wife and promoting tales. It's dirty.
Therefore it must be bad.

As posted previously by others, that grease heavy on
contacts is there for good engineering reason. First learn
how contacts make and break electricity before just wildly
speculating. But to make it simpler to understand: remove
grease on those contacts to make switch fail fast.

Stop 'feeling' a conclusion. Stop using old wife
reasoning. Or even better, first buy new switches, break them
open, and learn before posting. Or read the informed post by
George E. Cawthon. High current contacts require a heavy glob
of grease (or something equivalent) to last. Did you also
know there are two types of switches and relays? Some that
can break a current. Others that can only be switched when no
current flows. Only the naive would assume 'dirty' means
'bad' - just like myths from an old wife.

quietguy wrote:
This advice does not seem appropriate to me - grease on the switch
contacts is NOT a good thing - a little grease on the rocker is
OK, but only there.

I would suggest cleaning the contacts with CRC, apply a little
high melting point grease (silicon?) to the rocker bearing surface,
and reassembling.