A lot depends on exactly what goal you intend to accomplish, in the long run! Some products just clean, others also deoxidize, while others leave behind lubricants and/or films to prevent future oxidation. Ya gotta nail down what you actually want to do, before you can determine how best to do it!
I've found and tried the specific WD40 dry contact cleaner recently (which I never seen before, just the standard lubricant), that's why I popped in. Should be available worldwideI just use the RS supplied spray stuff for pure cleaning as it is residue free and then D100 (Deoxit gold) as longer term anticorrosion lubricant afterwards.
Blotting paper with cleaner between blades of switch contacts first then dab of gold.
Standard WD40 is a water displacement fluid not contact cleaner, but IIRC I have some WD40 contact cleaner somewhere.
Deoxit D100Having intermittent issues after switching between hi and lo sensitivity jacks. Hoping a little contact cleaner will address it, but I know they are not all =