First and foremost, the Corrado windscreen isn't a great design; a lot of experienced fitters struggle to get them right. That said the average windscreen fitter is not up to an acceptable standard and there are a new wave of 'techs' who lack experience and are totally void of common sense.
The issue is that the screen (sat on a bead of PUR adhesive) doesn't have much room between it, and the pinchweld. Getting the PUR bead height/pitch is the key to getting these right. Problems start when the average Joe Fitter turns up and panics, and hacks into the PUR with a knife. Furthermore, when the fresh adhesive is applied, they put too much on, and to get the screen to sit at the required height, it has to be pushed down which squashes the adhesive flat. A high bead wall then compresses down to a wide mess. The next time the screen is changed, the next fitter then has to do even more hacking - aggressive hacking - and so the problem worsens.
Another issue is the cutting back of the cured PUR which many used (and still do) long blades.
An experienced fitter can successfully remove and refit the windscreen. Unfortunately, there's no way of telling for sure what condition the pinchweld/aperture is in with the windscreen in place. You can carry out a water test to see how well it holds up against leakages, and to a degree, removing the A-pillar trims and pulling out the headliner bead can also give you an idea of how well/bad things are.
If you like the car, negotiate a price which will allow you to budget some cost towards any repairs which might be needed; a remove and refit of the windscreen at least. Dependent on who you use, you might be in for a new screen too as not all fitters can remove these screens intact. To be fair, these windscreens can be a real pig to get out, but not impossible.
