The B&K 440 isn't exactly a precision piece of equipment so I wouldn't worry about an exact value. Just well into the green would be fine.
Zoro is the cheapest place I know of for Slip Plate:
http://www.zoro.com/g/00058307/k-G2655791.
Grainger has it too for a little bit more:
http://www.grainger.com/product/SLIP...ilm-Lube-1WVK7