If you have a sunroof, clogged drains are the most likely culprit. VW/Audio vehicles with sunroofs are terrible for this... Another reason we got rid of our Mk5 Jetta TDI, didn't want it to start leaking again...I have a bad leak somewhere near the rear of my car and ending up on my passenger rear floor.my head liner is ruined and I literally vacuum about 2” of water off the floor board any idea where it is coming from?
With an aftermarket antenna, I would look at that first. Then search online to find the routing of the sunroof drains. If the tubes are clogged from debris they wont flow properly and the water will fill the tubes then pool around the edges of the sunroof eventually leaking into the car.I resealed the antenna because I have the shark fin aftermarket antenna. I checked the holes in the sunroof they look clear. I don’t know where or how they run down to the outside