I'm having the same problem with the clear splinter guard remaining stuck to my aluminum rails.
I have a number of different rails and the longer they go unused the more the splinter guard seems to become unstuck. All of the rails have the newer, see-through style guards and I've even purchased separate boxes of splinter guards and tried applying those without luck. When replacing the guards I use mineral spirits to remove any old residue and ensure that the aluminum is free of any grease or other contaminants that might impair adhesion, but alas, nothing's worked.
I do store my rails vertically, hanging from screws in the ceiling of my shop, as opposed to storing them flat where the weight of the aluminum rail might ensure the guards remain stuck in place. That's the only thing I can think that might help the adhesion process. If anyone has any ideas I'd be most appreciative. Some folks have discussed double-side tape, but could the extra thickness of that tape render the guard less effective? If not, what tape specifically would people recommend?
Oh, and hi everyone, I'm a long time troll, first time poster.............