I chucked the keys at Audi Worcester and said it was leaking...
However, I fitted a new bottle on my previous 8P, so if you want to fix it yourself, take the front right wheel off, peel back the arch liner, and you'll see the washer bottle mounted with a few bolts. Take them out. they're stupidly long if I remember.
When observing from the front right fog area after you're removed the fog light itself, you'll see the motor(s) in the bottle. Pull hard towards you on the motor(s) and they unclick from where they sit in the bottle, then pull up.
Pull off the flexi pipe from the engine bay so the bottle is free.
Then pull the bottle through the wheel arch liner and inspect it. put a couple of bungs in the holes if need be and fill it up with water.
If you do notice any leaks, silicone is only tempory fix, just buy a new bottle. Saves all this hassle again.
So if it's not the bottle leaking, then follow the pipes to the headlight washers and remove and have a look see.
Its worth having a look at the seals on the motors that push into the washer bottle, They might not look perished, but sling a new o-ring on there for good measure.