Yours is a later type mondeo right?

There were two types of screen fitted to that shape (not talking about heated and/or moisture sensor) - one with an encap trim and one without. The one with has a small "flap" of trim along the top coming from below the glass which lips up the aperture to the roof line. The later ones didn't have this and had "floating glass". All screens on all Mondeo's are bonded.

It may be possible to plug the leak with bond, either from the outside (provided there is no encap flap) or from the inside, but this will not be a full fix. And I say "may be" as there is no certainty it can be fixed unless it can be pinpointed 100% where the leak is. Even if the leak spot can be found, plugging it will not last forever. You have to understand WHY the leak has sprung. If it wasn't there from the factory, ie it's only just started, then doubtfull it's a hole in the glue. This would have leaked from day one. If it's a new leak, then the most likely cause is the bond seperating from either the body or the screen. This can happen for two reasons. 1) bad bond, 2) bad primer (a primer is applied to both the screen and aperture surfaces to "sandwich" the bond to allow a better surface grip). If the bond or the primer has failed and is letting in water, you can bet that over time more of it will fail and the gap will grow. Hence plugging it will only reduce the flow, not stop it.

Ideally the screen needs to come out. These screens, even the heated ones, can be saved and removed intact if you have someone skilled who knows what they are doing (ahem ) but it also relies on the fact the screen is not damaged in anyway. Even the smallest stone chips or scratches on the glass can cause it to break/crack upon removal and/or refitting.

If you have fully comp cover on it, you'd be far more advised to just have a replacement screen fitted by your local service registered to your insurance company (either Autoglass, National Windscreens, or AutoWindscreens) But be advised, do not telephone your insurance company asking for a replacement glass quoting that it is leaking. Lately the insurance companies have begun to refuse to replace leaking screens on cars over a certain age stating that it is "wear and tear". Of course the smart people go to the windscreen company, book it in for replacement and let the windscreen company sort out the insurance, as the insurance companies do not ask us why the screens are being changed, hence no lies are told and everything is above board