It's the "High Pressure Sensor" ... Partnumber should be: 5K0959126 and the O-ring has partnumber: 8E0260749
I know since I'm about to replace mine also.. No easy way to unscrew, I nearly broke my hand the other day and after that I nearly broke the motor :D .. So I'll be changing mine when I'm having the entire front end off to do the GTI frontbumper conversion.