All this talk of building a better burger encouraged me to go out and buy a kitchenaid meat grinder attachment. So last night, I tried it with some chuck and sirloin to make burgers. As we were sending the meat through, some gray grease looking stuff started coming out of the middle area where the grinding disk attaches onto the shaft. It got on some of the meat, which we picked out. But has this happened to anyone else? It was the first time using an attachment on my 5 year old mixer. Could there just be grease build up? Any thoughts would be greatly appreciated as we're planning meatballs for tonight!