Windscreen Leak

Hoping someone can help with my problem.
Water gets through the top of the windscreen and on inspection I find that the rubber seal along the top appears to have been stuck down but has now separated away from the bodywork.
How best to fix this?

Silicon sealant as sold in DIY shops for use in bathrooms is something of a miracle product for this sort of thing.  In a previous life, we used to use it to waterproof the instrumentation in a submersible vehicle capable of diving to 30m +.  Make sure everything is immaculately clean and dry and then apply a thin film before assembly.  It is available either clear, or in various colours.

I agree, I used
black silicone sealant around my windscreen seal, and it works really well, blends in with the rubber so it's not noticeable.

Many thanks for the advice.
I'll try the black silicone sealant !