Water leaks

[Tatsfield]

Vehicle windscreens are sealed with polysulphide sealants not silicone. Silicone will not last. Even poly sulphides do not seal without being placed between two surfaces, the screen and the flange, and put under pressure. Just putting silicone on the outside of a windscreen/flange leak will not work for very long. Which is why to reseal a screen that is leaking around the flange, as the V70/XC70 screens that were badly installed do, the screen has to be removed, the screen and flange need cleaning of old sealant and the whole thing needs to be reinstalled with the correct sealant. Which is why, if you have a screen leak, it is advised to take the car to a main Volvo dealer and strong arm them into getting Volvo to pay for the job.

[IAEB]

Tats. Silicone sealant releases acetic acid to cure, hence the pungent smell. Acetic acid is corrosive to any FE (iron) based substance.

Silicone is fine in your bathroom, it should never be used on a car.

[Tatsfield]

This is why bodging leaking screens with silicone sealant never solves the problem and merely makes it harder to clean up when the screen has to come out to reseal it with polysulphide. However trying to get polysulphide into a failed seal is an unlikely job. I suppose with the Volvo upper screen seal failure problem the screen might be able to be pushed sufficiently far from the flange to admit the sealant and if the failure was due to no sealant having been originally applied in the leaking area, it might hold and seal, but I wouldn't bet on it.