Vibratory finishing is what I do. But most of the stuff I do is on the industrial level. Normally for a job like that I use steel pins. They are good at "picking out" the dirt and grease. But most home level machines can't handle the weight of steel media. And pins are very expensive. You are probably stuck with using a Harbor Freight type machine and small ceramic media. You will need a soap too for the parts to come out clean.