Hi Bill,
The previous posters are right, the manual refers to using thin butyl rubber strips as the adhesive and sealant, whereas most modern windscreens I've seen are using urethane adhesive from a mastic gun.
Do you need to get it done by a professional ? It's all down to you and how confident you are in doing the job. There is no doubt that a competent professional will make a quicker and better job of it than your average DIY guy but that's down to experience and not because they're rocket scientists or it's a magical secret.
Your car, your call - IMO it comes down to how much you want to do yourself or if you like the challenge of learning new tasks, it's not about the relatively low cost of someone doing it for you.
Like a respray, it's all down to preparation. A sheet covering the dash/interior, carefully masking off areas where you don't want mastic to go, working slowly and not rushing the job. If you can do that, then there's no reason why you can't do it yourself. The Europa has a relatively small screen compared to modern cars and isn't that difficult to do, the biggest problem is setting it down squarely for someone working alone.
Full disclosure, yes, I've fitted mine but when our modern camper needed a new screen I had it done professionally - twice in fact, that thing was a stone magnet.
The first Europa replacement was shortly after buying the car because those butyl strips were leaking (SwiftDB4 is right, they're not the best idea) and the second time was a new replacement because the laminations broke down. I'd stuck it in with adhesive, it was hard work removing and I ended up cracking the glass. But neither time did it leak afterwards and that's from a period where the car sat outside in the Yorkshire winters, 24/7. In fact when I resprayed the car in 2011 I decided not to remove the screen because it was definitely stuck in and I knew I'd crack it getting it out. It still doesn't leak although it does look scruffy around the edges now....

Brian