Andrew, I have a machine also. I studied with Veronica Cass for a week in Florida. While the vibration, as David said is mainly for the old technique of leads they are still useful with dyes. I have my stroke intensity at about 15.
I live in Santa Rosa CA, 60 miles north of San Francisco so if you'd like to leanr how to negative retouch let me know and I'll teach you. You can learn the basics in a few hours, then it is just practice.