[Oreo]

I removed the bottom plate and the retainment pin, but I can't remove the body from the outer housing. I only can move it slightly back and forth and sideways, but not out of the housing. What's wrong?

From the picture, I can see that you only have 4 screws and the retainer pin. There should be 5 screws I believe. There is one that holds the outer housing to the BB containment thin rectangular chamber. At the bottom there is a screw that holds the spring in place while going through the outer shell.
I hope the photo I'm attempting to attach works. Hope this is answers your question: Imgur: The most awesome images on the Internet

Oreo

*Edit* I'm just linking the page instead lol...

 

[Oreo]

Right, thanks mate!

Now I'm stuck again - I can't remove the back plate. I can move it 2mm at any side, but it's getting pulled back in.

Surprisingly I never had a knock lever - is that normal? The rifle once worked fine and I never have seen this part before..

I have the Action Army Long Mag which has a knock lever, so I honestly don't know how to take that specific model apart correctly. You'll have to consult a more intelligent sniper than myself or be willing to experiment abit to find the answer.
Sorry I couldn't be any more help.

Oreo