Old shape 2007 is MKI. Never had emissions problems with any of my Octavias (had the lot now, MKI, MKII and MKIII!) and never put anything other than diesel in the fuel tank but my OCD means they've all been properly maintained i.e. oil & filter every 20,000 kilos (always before flexible service interval prompt), pollen filter every 40,000 kilos (OEM specifies 60,000), air and fuel filters every 90,000 kilos (as per OEM specification). The run home on the motorway could be a factor though, modern diesels do like to get out of traffic.