WD40 really isn't that awesome an idea for locks, mind you. Tends to congeal and gum things up if you do it regularly. Graphite powder is the stuff for sticky locks, although not sure it does anything about corrosion.
Have to disagree with you Shug, WD40 does not congeal in Vehicle locks, most of it evaporates, heavier Oils and grease congeals in Locks.
I have taken apart so very many Vehicle locks over the last 30 years that are siezed due to dirt and grime being attracted to the Oil/grease that some manufacturers use when assembling the Locks. In these instances WD40 helps breakdown any dirt/grime/congealed oil or grease and helps the (very) small springs in the Locks move the discs as they should.
Agreed, Graphite powder is the best Lubricant for Locks but only where there is no sign of Oil, Grease or water, Graphite used over a period of time in a concealed lock such as the Fuel tank lock will in the end hinder the working of the lock instead of helping.
WD40 will help flush dirt/grime out of a lock that cannot be dismantled for cleaning, it is amazing how much dirt gets into Vehicle locks over a short period of time. Some of the dirt could even come from your pocket. Our keys are not always clean when inserted in a Lock, some of the dirt stays in the lock when the key is removed.
Bugger, ive gone on a bit there...
Either way, lube the lock, I choose WD40 due to my experience.
Regards
Phil