my petrol flap is sticking

[MattInARedMicra]

I vaguely remember someone saying not to use wd40 inside the keyhole, because it will attract dust/dirt and stick again a few months later... but I can't remember what the correct thing people said to use is. Can anyone remind me?

 

[.Maarten]

I vaguely remember someone saying not to use wd40 inside the keyhole, because it will attract dust/dirt and stick again a few months later... but I can't remember what the correct thing people said to use is. Can anyone remind me?

Graphite powder