I'm another who will recommend against WD40.
In the past years it was a remove, clean & lube with the light oil on a lens tissue. Enough lube remains after the ring is wiped to clear up the problem & not hold dust, which is the original problem.

The drop of lube you use is mostly wasted since it takes so little to lubricate the ring. Actually most things in a camera. There are a very few latch points in most cameras or shutters where you may want to leave a visible dab of grease and fewer where you would like to have oil flowing around.