Hi, I just wanted to inform anyone who is interested, that this genuine item, from Skoda, is available from the main dealerships from less then a fiver, despite others selling them for a tenner or even more, PLUS postage. That is one heck of a mark up!
Anyway, I purchased one for my Fabia and it fits ok, just a little close to the bonnet cable, which with a little wiggle of the filler neck, means it will open fine but if you can't be bothered, opens with a wiggle. The cap opens to form a funnel, which helps prevent overspill of fluid, which often goes straight over the battery earth strap, on my car at least. I also slackened the earth, twisted it round on its fixing point (It was set at say, 12 o/clock, I reset it at 11.45). That gave just a little more space, too. (I was in the process of whipping off my battery and charging it at home, so had spanners handy). The silicone cap replaces the hard blue plastic one quite easily, with no need for any tools and takes just a minute but if you are fussy and want to move the bits I moved, it will take around 5-10 mins to do, at most.
I think they look a little hit and miss but in real terms, as do the normal plastic ones but they are a handy little bit of kit and may well fit other cars with similar sized necks. (50mm, I think and have seen on the 'Bay that they fit some Range Rovers, etc). Part number 6V0 955 485