I've had my Breville for a number of years. Great machine. In the past six months I've been having a problem with the grinder. It simply seems to struggle grinding. I have pulled it apart a few times and cleaned it thoroughly. Even replaced the felt o-ring since I was in there. Nothing looks wrong, but it just really struggles to grind. I use high quality roasts (nothing oily). The only way I seem to be able to grind is to drop beans in little by little while it grinds. This is a machine that has probably made 500 or 1,000 cups of espresso, without issue. Best as I can tell burrs don't seem worn. Any advise?