Did the 300 tdi and the td5 a couple of weeks ago, easy enough job, just re seal the sunroofs, also there is two plastic trays on each front corner of the metal sunroof which is bonded on with sealant, all four sunroofs i did had a gaps in the sealant so i resealed them too
Just get them taken out and pot rivit/ sikaflex some galv plates over the holes. Thats what I did to mine no more leaks hehe.
If you reverse onto the drive then the water will make it through the drain plugs but will not be able to make it out the tubes as they run back towards the rear of the car