If it's just the valve that is leaking it is both easy and cheap to replace.
Just notice you need a special tool for the valve as it is round with a notch so you can't use a normal wrench.

 

I checked all of the air suspension and it raises and lowers as normal, just a lot slower than usual. I will drive it down to the dealership and see if I can get it replaced!
Thank you so much!

 

This is what appears to be leaking, part number is 7L06168138B and you can see the notch the previous poster mentioned, each one of the air springs has the same part fitted.

Dealer part price is pretty expensive, so I doubt you will get out of it for under $300-400 for replacement.
I had the same issue so first thing I tried is to "nip up" the nut that holds the line which stopped the leak, if that dosen't work try cutting a little bit off the nylon air line to get a good sealing end for the olive to grip and try reconnecting to strut.

TonyB

 

This is what appears to be leaking, part number is 7L06168138B and you can see the notch the previous poster mentioned, each one of the air springs has the same part fitted.

View attachment 255034
Dealer part price is pretty expensive, so I doubt you will get out of it for under $300-400 for replacement.
I had the same issue so first thing I tried is to "nip up" the nut that holds the line which stopped the leak, if that dosen't work try cutting a little bit off the nylon air line to get a good sealing end for the olive to grip and try reconnecting to strut.

View attachment 255035

TonyB

Did your air suspension work raise slower than usual? If so did it hold pressure correctly afterwards?
And also did the compressor run more frequently when the leak was occurring?

 

I did not notice any change with suspension raising or lowering, being a while ago I cannot remember what made me check the pressure retaining valves but it must have been because the compressor lately seemed to be working more often.

Found a leak on one of the valves, when the line was moved side to side the amount of air leaking increased.
Removed the insert from the valve, replaced the internal 'O' ring and cut off squarely a bit of the air line and re-assembeled.
Not a problem with it since.
TonyB

 

I'm going through small dramas at the moment whereby I've noticed my compressor working more than normal. About 6 months ago, my front passenger airbag was lower than the rest and it apparently was determined that the airbag was faulty, so replaced both fronts, and it was still drooping in the front passenger side. The mechanics had my car for about a week doing tests and I'm still not 100% sure what they did but it may have had something to do with the air tank, but it has held up ok since, but to raise my car up, it is slow, and sometimes, my car can't make it to level 4 at all, and level 5 is out of the question, so maybe I need to tell the mechanic about these valves and to check them. Where exactly are they located if I may ask.
Thanks a lot.

 

The secret in trimming a leaky fitting is to ensure that the tube is cut square, there are a number of devices on the market that range from inexpensive to "its cheaper to get a new car", these are ideal and multiple uses Plastic Pipe Cutter - Suit 12mm to 22mm John Guest | CaravansPlus to ones that look like this picture . If you do decide to go down that path then make sure its a warm day because the hose does age and become brittle and end up cracking - replacement hose can be purchased from any industrial pneumatic hose supplier such as Air Fittings & Compressor Sales Brisbane - Parts | Fittings Express

 

As people have said, most likely a leaky retaining valve not holding pressure. Wheeler Dealers did a repair on the Porsche Cayanne suspension (same as Touareg suspension from what I'm led to believe).
Check this link out - it may help.

Cheers