I must confess to being a bit confused about your pump. The filters on Juwel's website all show the kind of pump I used to have. Look at this
http://admin.juwel-aquarium.de/out/media/Pumpen_bioflow.pdfI've got my old filter out of the cupboard. The pump says Pump 600 GB on it. My pump housing looks like the right hand side of the flow chart on page 1 (the side labelled Typ 400 etc). Scroll down to page 4 of the link, and that's what mine looks like. As you can see, the pump fit at the top of the filter. The divider has a tube running down one side of it, and the pump clipped onto the top of the tube.
I got my tank in 2006. The tube attached to the divider runs the entire length as shown on page 4 of the link. The newer design came in shortly after I got mine, and the tube starts a few inches down the divider - see page 3 of the link.
The divider in the manual for the pump you have does not have a tube attached. There is a holder in the bottom of the filter than the divider slots into, and the pump slots into the holder as well.
Can I ask, does your divider have a tube attached to it? I can't see the top of a tube in your pics, but it could be that you have the newer type than mine with the tube starting a couple of inches down (like page 3 of the link)
In other words, I'm asking if you bought the correct replacement pump?