Replacement part probably costs less than £10, so I'd just get a new one.
If you really must attempt to revive the old one, I'd remove it, douse it in lighter fuel, click it a few times, wait for the switch to dry out then re-fit.
They really seem to be quite cheap those switches.
On the other hand, I'm working on a cheap Baleno I just bought and there are quite a few little fixes to do. So, I'm trying to manage with as little money as possible in order to keep the price of the car from doubling...
And it's kind of fun trying to fix things with minimum budget, now that I have a second car that dare to play around with... Never before have I added engine coolant, let alone changed oil...
Anyways, if there doesn't seem to be any well known tricks on this, I'll probably go by your recommendation.
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