Tom, Geoff, thanks for the invaluable advice. I would have baked the gasket with a hair dryer left to my own devices. Top l/h side of the crystal in my first pic, you can just see a big piece of the crystal is missing. As soon as i applied any serious pressure the old crystal broke but luckily the plastic gasket was sound. I has some silicone lubricant spray and applied the slightest smear around the gasket to aid re-fitting of the new crystal. I then applied the same to the pushers with a tooth pick.Amazed at the crap thats in there. For the record, the piezo alarm sounder just sits there under the weight of the module. Anyway , job done. Many thanks
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