I don't use WD40 as a lubricant...
What I do use is either a teflon spray:
http://www.amazon.com/DuPont-Non-Sti...ptfe+lubricant
Teflon goes on wet, but, dries leaving the teflon coating. Since it is dry, it doesn't attract or collect dirt, but, what I use the most is Slip Plate; a dry graphite "paint in a can" that you spray on and let dry:
http://www.amazon.com/SLIP-Plate%C2%...rds=slip+plate
Slip Plate is what I use the most...stabilizer screws, slide out rails, steps, even the pin on the 5er's hitch. Even as it "wears" off, it leaves behind a coating of graphite, very dry and very slick. I tend to use the teflon for door hinges, locks, latches, etc. and I use the Slip Plate for "heavy duty" outside things that I want to keep sliding without getting gummy or collecting dirt and grit.
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My 2 cents, your mileage may vary...
Don
Bronwyn
2 Cats; J-Lo and Ragamuffin
2011 Keystone Cougar 318SAB
2011 Ram 2500 Longhorn CTD HO
Built in brake controller and exhaust brake
Tri Glide TrailAir Pinbox / B&W Companion Hitch