It’s the oil of wintergreen that softens. Alcohol is just a carrier. I restored a set of the rubber grommets for the intake valve cover. They were rock hard and now are minty new. Make the mix in a plastic container. Place part in and leave it alone. Make sure you cover it or the alcohol will evaporate. You may need to leave it for several days, just check things daily. Remove when it looks good.
You can overdo it. I left some stuff in for an extended period to see what would happen and it started to swell.