Ray White is an excellent teacher. I took his beginning and advanced classes and received a really good grounding in what to do and not do, despite having done some of the servicing on my machines for years. Since then, I've tackled many machines and have yet to find one I couldn't fix. Ray is retired and travels to teach, but that may not last forever, so I recommend you find one of his classes and go. Here is a link:
http://www.whitesewingcenter.com/index.php
I went to New York (from Massachusetts) to get this training and, believe me, it was worth the trip. I advise you to go wherever you need to get his training. He is a VERY good teacher and a really nice guy.
Cricket