Jim,
Most adhesives are based on some form of synthetic rubber and are easily removed with lighter fluid (the kind you use with, say, a Zippo lighter). Lighter fluid "usually" doesn't hurt stuff like car paint under it. But I have no idea what it will do to your 20B. I'd only use this as a last resort if the milder stuff doesn't work.
If you can risk it, test a drop on a Q-Tip on the back to see if it hurts the plastic before you go after the front. Keep it out of the key holes and away from the clear part over the display if at all possible.
Again, only as a last resort!
And things like toluene, MEK and acetone will undoubtedly ruin the plastic. Definitely don't go there!!!
My summer jobs during college years were at a manufacturer of self-adhesive papers, films and foils. Amazing what you learn when you're just a go-fer.
For those of you considering removing your WP-34S overlay, be careful to do the following for best results:
1. Pull away at a right angle to the surface; don't peel "back", but "up". "90-degree peel adhesion" requires the least force.
2. Go as slow as humanly possible. It's a "pressure sensitive" adhesive. You are applying "negative pressure" to peel the overlay. The force to peel cleanly depends on how fast you peel, but the force to break the plastic film is fairly constant. To avoid breaking, GO SLOW, thus keeping the peel force less than the tensile strength of the label.
Some adhesives are designed to be stronger than the substrate (film) they're on, rendering them "tamper evident" or "tamper-proof" as the film shreds without lifting the glue. Not much you can do with these. But I don't think that's what Eric used. Tamper-proof stuff is usually used for price stickers, labels on pharmaceuticals, stuff like that. Eric used a pretty strong, heavy label substrate. (Good choice -- easy to pick back up and realign if you start a bit off alignment, at least before the final "roll-down".)
Dale