This DIY will hopefully help if you are to tackle a coolant leak that is most likely coming from a plastic flange on the back of the engine. The flange is known to either get a crack in it or the o-ring that seals it to the head starts to leak (which was the case with me)
Start by removing your whole airbox to give you some room to reach around the backside of the engine.
Here is a pic of the part and you can see where the red arrow points to the problem I had. There is a channel that the o-ring sits in, and the inner wall of the channel deteriorated and allowed for the o-ring to move and not seal properly.
Part # 06B-121-132-E $29.77 This was from a VW dealer when I told them I needed a flange for the 1.8t Passat. The flange has a little bit different look to it but everything you need is the same. It will be a little more expensive from an Audi dealer and the number should be different.
As you can see there are 2 hoses that connect to it 1 coming out toward the driver side of car, this one is held in place with a squeeze clamp (squeeze the ends to make it expand to move out of place) The other hose goes directly down and this is a quick diconnect. For this hose you will pull a little wire clip and it will move out of the locking position but will remain attached to the hose, you now can pull this hose off.
To free up some space you will remove a few things (rubber oil check valve, which is the piece that has 2 hoses connected and is connected to the head) and disconnect some hoses and plugs (2 plugs [1 is connected to the coolant temp sensor in the top of the flange you are removing] [other is shown in the pic with arrow, this may just make it easier to move wires around so you can get back in there] (arrows point to things that can be removed) In the picture they all have hose clamps but yours will have 1 time use clamps that you will have to get off then replace with hose clamps.
You will need to undo the silver oil feed line to get it out of the way of the flange (piece you are replacing) and also the small black metal line above it will need to be undone to get the flange off. You can see in the pic the silver line is fastened with a 10mm nut over its bracket, also there are 2 6mm allen bolts that hold it in place on the side of the engine above the turbo manifold. Once you slide the bracket off there will be a 10mm bolt that holds the flange in place. The same goes for the top of the flange with the black line which I couldnt get a picture of. 1st the 1" black tube that is sitting vertically will need to be taken off the stud you have undone the 10mm nut on, then the little black lines bracket will need to be slid off this stud, after these are removed then you can remove the 10mm stud that holds the top of the flange in place.
1 last thing you may have to undo the 2 1" black tubes that run along side of the motor above the turbo manifold to slide things around. These are held in place with 5mm allen bolts and 1 10mm bolt
[the 2 studs that hold the flange in place have a threaded shaft on the top of them which is what the brackets you are removing are slid over]
You should now be able to remove the Flange and swap the coolant temp sensor to the new one (dont forget to swap the o ring for the coolant temp sensor, or even better get a new one) The sensor is just held in place by that little clip.
Now just go in reverse order and put it back together