Kitchenaid Epicurean stand mixer KT 2651 XHG

This mixer was a gift to me from a friend in California who purchased it from Williams-Sonoma and shipped it to me in Georgia. The gear box has always made a loud grinding noise, however, it has always worked properly, just noisily compared to other Kitchenaid mixers I've used. Additionally, even from the beginning, the speed selector would be moved to a speed setting (any setting) and nothing would happen. I would just leave it, say, on the 3 setting. In a few minutes, the mixer would eventually come on and start mixing. I took it to Williams-Sonoma in Alpharetta, GA and they basically said I needed to send it back to California. Well, I have put up with the noise and the intermittant speed control for at least 10 years. I'm tired of the sorry service from this mixer and want to get it right. I can repair it if I can find the parts. I would like to know what to do. In my family (mother, brothers/sisters, nieces/nephews, we own 11 of these appliances but mine is the most expensive and gives the poorest service. What to do??!!