You will have to pull your headliner down to repair this. Your sunroof sits in a metal tray and when water drains out of the sunroofs it goes through two black plastic blocks on the sunroof tray. These plastic blocks have hoses that run down the inside of the "A-Pillar"(the windshield frame is a part of this).
As I said, the blocks are plastic and the sunroof tray is metal. The silicone seal was poorly installed when the Rover was built and will need to be resealed.
I just went through the same thing and I fused it to the metal tray with JB Weld Plastic and then covered that with clear silicone sealer to keep the water out.
Its a pain in the neck to get the headliner out, but its your only way to solve this problem.
Hi I have a leak that seems to be coming in the sunroof its very bad during heavy rain, and I cant open the sunroof because the electrics are gone from all the water getting in, is there any way I can open the sunroof the check the drain holes and see if they need to be cleared I have a TD5 Discovery 11 automatic and there's so much water now i'm afraid it might fry the electrics for the gear box as well any help as soon as ye can thanks