Regardless of what Electro Detective says do not use WD40 in a multimeter especially. It is not a dielectric lubricant, will attract contaminants and can cause the safety rating and accuracy of your meter to go down. It is one of the worst things to put inside your DMM. It is also flammable. Do I need to say more?
More anti-WD40ism
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If OP applies it with a cotton bud, it's only the LIGHT lubricant that will remain, to ensure minimal selector track friction,
and adequate contact till OP can source an appropriate lube.
LIGHT lubricant means it won't attract any more contaminants than any other lubricant would,
and nothing is going to catch fire unless your suburb gets napalmed by a nest of mutant fireflies,
or the multimeter gets tossed on the BBQ along with the usual cadavers during an after work beer binge session.
Try it for yourself on any similar material/s and plastics before taking the plunge,
it smells like petrol yes, but that soon goes away.
Do a metal to metal resistance contact measurement as well, and see what happens.
There is way too much WD40 paranoia, it's not an aggressive product as some others,
and common sense dictates if you've got nothing else to bail you out,
it's better than nothing