Recently had the rear wiper motor on my '08 octy vrs estate pack in. Had a new one fitted but when I picked up the car and checked the wiper action the central portion of the screen was not being cleaned. I mentioned this to the mechanic who took the arm mechanism apart and re fitted it with no luck. The head mechanic had a look and told me the arm spring had gome and that a new one was needed. I replaced the wiper arm and fitted a new rear blade myself and still the wiper doesn't clean the middle third of the screen. Any ideas?

Ok, I'm guessing a bit because I've never driven a Mk2 estate in the wet. Did you get a new blade fitted at the same time? Lots of aftermarket blades have difficulty conforming to the compound curve glass.

Yep I fitted a new blade when I fitted the new arm it was a flat one. but the original blade also didn't clean the central portion of the screen

The OEM rear blade on the estate is different to anything available aftermarket, even from Skoda dealers! Your only hope of curing this completely is to physically go to scrappies and look for an estate with an OEM blade.