Personally I would guess it is not OK as I figure there is always a
thin layer of oil but several people I have spoken to say that they
use WD40 all the time.

WD40 is a mixture of kerosene and light spindle oil, not much good
for cleaning since it doesn't evaporate at any rate that would leave a
dry surface in your life time.

And oil turns to varnish over a longer period of time.


Referring to the Material Safety Data Sheet and other sources:

WD40 is 70% Stoddard solvent, a controlled-flash-point kerosene.
WD40 also contains 20% petroleum-base (paraffinic) oil, and less than
10% proprietary corrosion inhibitor, wetting agent, and fragrance.
The aerosol cans add 25% isobutane/propane propellant.

Over time, the paraffinic oil will react with atmospheric oxygen
and polymerize, creating what is technically termed a "gummy mess."

If you want a solvent, use a straight solvent. If you want
lubrication, use a good oil (they do vary in resistance to oxidation).
If you need to clean and maintain electrical contacts, use a product
made for that purpose.

Regards, Alan