Have you a supply of perfectly good bottles that aren't being used because the rubber sealing washer has perished? Join the club! Finding replacements is NOT easy! However, I have found a company that supplies O-rings that do a wonderful job. Furthermore,
these are sulfur dioxide proof! I used 20mm by 5mm but they were ever so slightly large - even though they worked perfectly. A better size would be 19mm by 5mm. The material used is: CS EPDM 70 ShA
Here is the link: www.polymax.co.uk
If you wish to write to them their address is: Polymax, Building 90, SEME, Budds Lane, Hampshire, UK, GU35 0JE