I'm sure that you have it open by now, but one common culprit is soft drinks
which slosh over and the dried sugar causes sticking. The WD40 rec should
work, but also a simple light water spray to dissolve the sticky material.
Once you get it open, that is the time to look it over carefully and clean it
out, or it may continue to stick. Depending on your access, you can place a
paper towel in places where you spray to absorb the water, so it doesn't run
places it shouldn't. If you have clear access, just wipe the surfaces/edges
with a damp sponge.