Hello, folks.
Steph, there is no really secret areas in Zulag 2, 3, 4. If you read those storystones (those devices that Abe puts his hand to read information) you will find all the mudokons on these levels. The real hard to find are in the first time you go to stockyards (about 12), and there are some in the Temples of Scrabania and Paramonia (9, if I can remember correctly).
Doug, you are doing a great work helping up people with Abe's adventures, with clear and mature answers. It reminds me when I was assigned the help forum moderator, a year ago, mostly because I used to do same thing.