Hi all, 2002 A4 Quattro 1.8l turbo

This car is my stepsons. I believe there’s a leak at the passenger front but I cannot find the leak. The red Brake light indicator keeps blinking on the dash with no beeps. The reservoir empties after driving. He keeps filling it up. I have pulled the front passenger wheel to look for the leak but, it’s dry. All other wheel appear to be dry, however I can see that it’s wet between the passenger front door and the front wheel well on the inside of the body. I suspect it’s the hard metal brake line but, I cannot trace it. It’s as if the line goes into the body of the car and it’s looks as if it cannot be accessed. I’m hoping to cut and repair the line but, I can’t find it and I don’t know how to access that area. I’ve pulled the wheel off and had the car on ramps and it’s too difficult too see way in there. We are at a point where my stepson is putting fluid in the reservoir every time he stops at his destination.
I would like to fix this before it gets too cold here in update NY. I would greatly appreciate if someone can tell me what to do or have a diagram of the brake lines so I can trace the lines.
Thanks in advance.