You should replace the group gasket (MC047SIL) and screen (MC137) every 6 months, if you leave it longer the gasket will get hard and will become difficult to remove it from your machine, when you do eventually change it. You will also need the following seal which is included in this kit MC195. see diagram image.
Parts included in this kit:
Kit is suitable for the following models:
This Lelit guy will show you how to replace the group seal and screen.