Maybe worth checking out this adhesive from Reprolables. I have some peelers, reissue G1 and Platinum Predaking. All I want is a quick 'new' adhesive to give the sticker some 'stick', and won't damage the a) sticker or b) the plastic.
Let's share our results!...beats having to track down new stickers, in any case. As for the future, I now give a quick q-tip and soap solution to any plastic surfaces to ensure you're giving the sticker the best chance to adhere. But storage, humidity, all seem to play a part in unsticking that what was once stuck