I believe I posted this once before. I figure it's worth mentioning one
more time...

The shelves in my Westy were pretty grubby when I bought (outsides were
clean, but coffee spills and other stuff made the insides look less
than pleasant.)

When I was working on my fridge on Saturday, I also took the time to
remove some more of the coffee tar dirtied shelves for cleaning
purposes.

Now coffee isn't so bad (water and patience will remove it mostly).
Some of the other stains are a bit more difficult. I use the Gojo
pumice hand cleaner, A gentle scrub and then a rinse and dryoff (you
don't want to soak the plywood, but a little bit of water that is then
dried off shouldn't cause any long term problems.) and now my shelves
look as good as new.