[Barrio773]

Where are the drainage holes for the sunroof?
Mysunroof has started leaking on my 92 416gti and the roof liner is getting wet.

[Plodder]

The drainage holes in the sunroof tray are in each corner of the sunroof tray.
The two rear drains are behind the interior side trims in the boot. Take care removing these trims as they might be a bit brittle with age particularly around the bottom edges. The front ones drop down to the inner wing via the A pillar and you can feel them if you put our hand behind the interior trim in the foot well just in front of the front doors about 250mm from the carpet. The pipes drop down from the sun roof to a rubber elbow which ships the water through the panels to the outside. The front ones can be seen by removing the front wing liners.
My elbows we’re in reasonable condition but I brought some replacements from rimmers. However these had not stood the test of time in storage and were only marginally better than the existing ones but also required sticking along the seams where they had perished.
See Johnny 216GSI comments about debonded windscreen if you have water under the carpet. I had exactly the same symptoms and spent years trying to trace the problem as well only also to discover a number of places where the windscreen had debonded . A debonded windscreen can also cause corrosion under/around the mastic which can result in expensive repairs if ignored - I speak from bitter experience as a large chunk of my restoration costs have been spent on rectifying such a problem

[Barrio773]

Luckily no water in the footwell, just the headlining is damp

[Plodder]

Thats good you have no water in the footwell..
Im hoping to do the headlining in the coming year and will change the drainage pipes and service the electric sunroof at the same time so I currently don’t have an experience in this area at the present time to pass on.
Good luck

[4V8s]

Sounds like the drains are blocked.

Tracing leaks is indeed a nightmare on any car so you're lucky its obvious!

I would on a dry day open sunroof, park downhill then pour water into the area of each corner and see if it drains ok. Similarly rear parking facing uphill

Once you know which one or maybe more than one is blocked, in the past sending a steel wound cable of narrow gauge eg from inside a bike brake cable might dislodge the blockage, but personally with old cars i think this is risky.

I wonder if there is some product out there, or something like mr. Muscle drain unblocker that might work?

[Plodder]

The drain pipes run into rubber elbows in the bodywork to allow it to drain out through the panels.
The outlet of these elbows have a restricted opening and wont allow debris to pass out . One of mine was blocked with debris after being stored under a tree for several years.
Suggest you check these. The rear ones are behind the interior trim in the boot so are easy to get to. The front ones are a little harder to access due to their location.
I checked mine on a flat drive with a watering can and carefully poured a small amount of water towards the front and rear of the sunroof tray on each side. Don’t flood the tray too much if you’ve got a blockage
You’ll see the water running out from under the car behind each wheel arch . No water then thats likely to be where your blockage is.
A photo of the rear elbow and some of the debris I found