whilst maccapacca is basically correct i think he has exaggerated the problem a little bit
If the intention is to keep the cinq for a long time regardless of it's problems then i suggest the following.
the rust will be worse under the windscreen rubber, but at this stage i feel it might not require welding. But simply sanding back the paint flakes and using some kurust will do nothing to prevent further damage, because it's started under the rubber.
It looks like it doesn't have a bonded in windscreen, which is a bonus because you can remove it yourself and repair the damage then refit the windscreen (you might want to get a professional to do this for you - an independant windscreen fitter will do that for a few quid)
But assuming you don't have time for this now, then the best thing you can do is to lift up the windscreen rubber as best you can. scrape away any loose flaking bits, then spray some dinitrol 3125 under the rubber. You can get this in an aerosol with a little tube on the end. that will kill any rust it finds and it will creep along seams and is basically 10x better than waxoyl. the last can i got from halfords but i don't think they do it anymore.
while you are at it, you may as well spray some under the whole of the windscreen rubber. then what's left can go in the wheelarches, and anywhere else you think there might be rust.
wipe any excess dinitrol off the paintwork with white spirit after you have finished
the windscreen rubber has a rubber insert in it, that you can remove to make it easier to lift the edge of it up. (the insert is meant to help lock the windscreen in place after it is fitted.)