I'm having a heck of a time taking a fiberglass csting off of a plaster plug. I've tried a layer of primer, two layers of PVA mold release with a layer of paste wax for good measure and still get too much bonding. In an earlier thread someone mentioned a mix of vegetable oil and soap. Is there any other way? Frankly I've not any patience left for another failure. There's got to be an easier way! People do this every day. What's the secret?