Where does the pressure control of the AGR valve come from at 2.5 TD (X25 DT)?

I’m afraid my AGR valve is broken. Had had an oil stain under the car every day a little bit a year ago, but there was no oil loss. The whole engine was oiled. My alternator killed the oil. After the TÜV had warned about oil loss and I had an engine wash done, there was no oil for a long time. Now there are small oil splashes over the alternator. Fits to the AGR valve. I’ve been rummaging here for a long time and seen a photo of the AGR. There’s a hose on it, I don’t, the nipple also looks as if a hose has to be on it. In the meantime, I’ve read: The AGR is controlled by mechanical pressure box, the exhaust return should only be active at partial load. Therefore, a pressure line to the pressure box, which informs the AGR of the current load situation. My question now: Where does the pressure signal for the AGR come from? Maybe the hose still hangs around and has to be secured. Otherwise, I have to replace it, even if the AGR valve is replaced by the AGR without an order signal.