3 years ago, I bought my kitchen aid mixer and a whole boatload of attachments for $50 in an estate sale. I think it is the best use of $50 I have ever made. The owner's best guess is that the mixer was about 30 years old. It is running very well but when I change the speeds some of the speeds do not seem to be any different from one of the lower speeds, i.e. 2nd and 3rd sound exactly the same. Is there a way to rebuild this mixer?