2004 T5 2.5 174
Your EGR is a strange one. As you say it's different from the standard EGR for your year. I've never seen one with that nut on it on a VW. It should look like the ebay one in your pic. The silver part is the diaphragm for the EGR and needs a vacuum supply from a small EGR control valve (similar to an N75) to work. The black plastic chamber (at 11 o'clock in the yellow circle) is the changeover valve/manifold flap which closes when you switch off, that has the correct supply but I can't see a vacuum supply for the EGR where it should be at all! I would take it off and check that the EGR isn't stuck open.