Our own group gaskets made from food grade FDA silicone. Unlike regular gaskets that are made from rubber these do not have any smell or taste whatsoever, and are easy to change since they will not bake rock hard like rubber does. If you have ever struggled to change an old gasket you cannot help but notice the awful smell and the black soot that comes off the rubber. And that is what you are potentially consuming with each drink.
We have spent months testing and adjusting the material so that these have the same compression strength as rubber, but are also softer so that it is easier to create a good seal.
Our own silicone gasket for the Breville 58mm models. Those models should be BES900XL BES920XL BES980XL: SGS food test report
Size for E61 8mm gasket: 73mm x 57mm x 8mm (Red colour): SGS food test report
Size for E61 8mm gasket: 73mm x 57mm x 8.5mm (Blue colour): SGS food test report
We have found that the replica E61 groups made these days are pretty much all the same, the different machine manufacturers then use either an 8mm or an 8.5mm group gasket.