In article .com,
"Russ" says...
Tkanks Dave - the key isn't stuck - when I turn it in the lock it
doesn't engage and therefore unlock. Any ideas?

What Dave said - wiggle a bit from side to side too. The most likely
cause of your problem is that the pins/plates have gummed up or
corroded so they no longer slide freely. The WD40 should help to
free them up, and wiggling the key helps to work the WD40 into the
mechanism.