LDV Convoy roof fan leaking

Picked one of these up recently to get around with the family and with the recent wet weather have noticed it's not quite as watertight as we'd hoped!
The worst leak seems to be the ceiling fan/vent at the rear which yesterday we could have showered under as it just dumped a load of water into the back of the car as I pulled off

I've had the plastic cover off underneath and can't seem to determine exactly where it's leaking. One thing I did notice was that the front stand-off that the screws sit into is snapped off so comes off with the cover. I have tried using silicone sealant around the edge of the fan and even tried to plug the hole where the stand-off came from last time but it doesn't seem to have helped so wanted to check if there is any other common water ingress points I'm missing from that area.

Have also had smaller leaks from some of the rear windows which seem to have stopped leaking as much after some sealant was applied and a small bit of water coming in the side behind drivers seat which is making the internal light wet however I understand that might be a failure in the roof seal so will be getting a better look at that once it dries up.

Thanks in advice for any help!

Water leaks came as standard on an LDV, I had a new one years ago and that leaked from day one

That was one of the minor issues........ Gearbox falling out was more serious...

I've had three LDV's , all pilots or Sherpas , and must have been lucky as they've all been bone dry. That said I've driven Fords, Citroens and others that have leaked and the common factor has always been when the van has been fitted with ceiling fans or roof racks of some sort. Puncturing the roof never seems a good idea. If it were me I'd look at getting rid of the vent. Perhaps visit a scrap yard and see if they will cut you a section of roof panel i.e so it's the same profile and fix that over the hole.