like Bogan said WD-40 is not oil
I know that in my manual of my fork is clearly states that you need to oil the bushings with a tefon based oil (bushings are the rings around the inner legs so where the inner legs go in the outer legs

) it also stated that you should NOT use WD40 (it really said it by name)
so ask your bike store what to do... hopefully they fixed it at the check.
my advise is, get a bottle of teflon based oil. you can use it on your chain etc.
can you it almost anywhere on your bike.
but do use it mildly.. and clean stuff before using
