2Silver, you can get a feeler gauge at an auto parts store. They'll know exactly what you're talking about. You can use them to make sure your rollers are perfectly parallel all the way across. When you need adjustment, that's what the little gears on top are for.
Actually, if you do a lot of form folding, you can adjust one side or the other to achieve a deliberate curve, or to squish the folded side the same as the unfolded side.
If you use pattern rollers, the kind you have to change out, you absolutely will need a feeler gauge. Yes, I have used my pattern rollers. 46th Street Jewelry Supply in NY has a large assortment of pattern rollers for the Karat mill.
Metalliferous out of NY has a good selection of brass plates, and if you go together with several other people, you can get a good price break. You can also etch your own plates.
If you want more information, you can go to the Durston site and download the user's guide. It has much of the information in the Goss' site, but is more professionally done for a print version.
http://www.durston.co.uk/lan-en/online-guide-p1-en.htmThere are just so many ways to use a mill that it will soon be the most important tool in your studio, other than the torch. I collect material from all over to use in my mill--fabric, papers, netting, cheesecloth, wire, screen, leaves, die cut patterns--just to name a few.