I would just keeping to sanding them. Not sure how a form of liquid would react to the slate. You would have too really do allot of sanding to over do it. You basically just want too roughen up the calling surfaces so there should not be any need for heavy sanding. I use a Scotch Brite pad on my slate and a piece of wire screening on my glass.
For my slate, I do a little sanding with a rough grit on the striking surface. Same with the acetate peg in a figure-8 motion. I see no practicality in alcohol unless it’s a celebratory cold one after a kill. Slate is a call that will work when wet unlike a box call. I’ve never used glass. As far as a diaphragm calls – store them in the fridge or freezer. They will last for decades. Leave one on your vehicle dashboard in the sun for a day and it will disintegrate.