Does your Fabia have a DPF? If it does, and you have been making short journeys and interrupting regenerations, the oil could have been contaminated...
Was the egr valve changed for a Skoda one? With so many being fitted to "fixed" cars, in quite a few cases pattern parts have been fitted and failed....
I don't have a unit with Sat Nav, but have read of problems caused by the latest software update. I know of at least one owner who is holding off the...