Our office has installed new whiteboards over the last two years. Many of these boards are heavily used and have already devolved to the point of being useless -- the writing on them has become all but permanent and they are heavily stained.
I've found that simply cleaning them (with a household cleaner, such as Simple Green) goes a long way toward keeping them in a usable state. After cleaning, much of the marker (80%-ish) can be simply wiped away, but there is still a strong "ghost effect" remaining.
I've tried commercial white board cleaner. It's about the same as household cleaner, but is more expensive.
I've tried both WD-40 and car wax (Turtle Wax and Rain-X), as recommended by various sites on the internet. The car wax does not seem to offer much improvement. The WD-40 is the better of these two solutions, but leaves the board a little greasy, and the markers tend to smear (only a bit) when wiped.
What is recommended maintenance for keeping the boards working well? And what is the best way to recondition a damaged whiteboard?