I decided to try a silicone gasket for my Silvia after having a bad experience with a string of non-OEM rubber gaskets that seemed to disintegrate all too quickly. The genuine Rancilio ones seemed expensive and hard to get hold of in the UK without spending a fortune on postage so I decided to try something new.
I discovered the Silasket gaskets through a coffee forum. These gaskets are made with Silicone not rubber and are intended to last a lot longer than the standard oem gaskets.
Fitting was straight-forward. After removing and the old gasket (and some cleaning) I lubricated the new gasket with a bit of mineral oil (Note: soybean oil is recommended by the OEM) and fitted it in place. Initially I didn't use any of the shims that were provided, but I quickly realised that a shim was necessary. Fortunately due to the oil the gasket was easy to remove without damage and I added a shim to ensure a good fit.
The shims are included with the gasket and are used to ensure a good fit and to allow for any wear you might have on the grouphead lugs.
I've had the new gasket on the go for several months now and it's working a treat; no leaks and still looks to be in good shape.