Isopropyl alcohol is my magic solution to all things grip-related. It can be used as a lubricant to get them on and off (best trick there is to use an aerosol can of the stuff, designed for cleaning electronics, and squirt it under the prised-up-with-a-screwdriver end of the grip, then massage it around until the whole thing is loose), but should also do a good job of cleaning away any oily or otherwise gunk that may be acting as a lubricant. It'll evaporate completely in a couple of hours, hopefully leaving the grip solidly in place.