I've got a Microsoft trackball that's 6 years old and it's served me very well (in use 8 hours a day, 5 days a week - 11500 hours!) but trhe finish is getting a bit tatty and i'm having to clean the ball almost every day now. Does anyone know where I can get a new one? Found a few by Logitech and other companies but i'd rather have a microsoft one if they still make em...?