Quote: Originally posted by Mik+Lynette on 23/7/2012
...I am going to silicon seal it all from the outside, as in seal it closed so it cant be opened till i can get a new one
You'll need a fair bit of silicon then. These are designed to permanently vent and can't be sealed, but your leak (if it is the rooflight) is more likely to be a breakdown in the existing seal and won't warrant a complete replacement of the fitting.
See Jeff's link, these are a straightforward job to remove, clean-up and reseal/refit.
As for the roof, you can't comment until you've seen the full extent of the ingress and this will be better seen when the rooflight's removed.