Hmmm, yes. Presumably the windscreen was replaced at some point and they never did the seal.
Where do you go for parts generally? Do Fiat still have them or do you go to Ricambio?
Parts for both Cinquecento's & Seicento's are starting to get a bit thin on the ground but if you know where to go for parts you should be ok Ricambio is good for Cento parts, Fiat's a little hit & miss depending if you have a good dealer nearby who knows what they're doing as most of them don't, also eBay can be surprisingly good for NOS parts. The parts suppliers I generally use are
:
Shop4Parts, forum favourite with 10% discount on every order if you
donate to the forum
:
Ricambio, have a good selection of Cento bits
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Italiparts, really good for hard to find genuine NOS parts which you will find with Cento ownership

:
DG Rally, X1/9 Specialist who sells through eBay but quite often have genuine spares for us Cento owners
: Dr Auto Ricambi, This company are in Italy & sell on eBay only selling genuine parts but as you'll find out with Cento ownership some parts are not obtainable in the UK anymore so you'll sometimes have to buy parts from Europe, when I changed my clutch I needed a new shaft cover which goes on the gearbox end of the offside driveshaft & holds the inner boot in, someone who'd worked on the car prior to my ownership had bent the cover, I couldn't find one anywhere in the UK but Dr Auto Ricambi had one so I ordered it & it was delivered through my door 3 days later from Italy, I've since ordered some other bits of them & they don't fail to impress.
: Fiat, This is usually 2nd to last resort before buying from Europe as like I said at the beginning of you have a good one nearby who knows what they are doing then it can be really good apart from some of the prices

but some like my local one just aren't interested as I went into the local one to me a while ago & as soon as I gave them the reg they instantly said "it's too old we won't have it" whereas where I used to live the parts man at the nearest dealer was just brilliant all you had to was given him the reg & part number of parts required, he'd sort it & say it'll be here in however many days, so Fiat are a little hit & miss