Always a good idea to have it checked out via AA etc or at least HPI it. Great cars (had mine nearly 3 years). Running costs aren't bad and volkswagen have just introduced good value fixed servicing costs. Recently had them do my MOT for £30. I get 34mpg average and recently had over 40mpg on a long run. Should run on super unleaded, which costs more. Always run mine on Shell V-power or Tesco 99 and I think this is what most people use. Also running cost can depend on what service schedule, longlife or time distance. Be aware of white worm problem on 18" wheels and refurb costs. Tyres £100+ ea for decent rubber. Get approx 12K miles from my Goodyears. Check for condensation/water in rear tailgate spoiler brake light and headlights. Check for wear on driver seat bolster. Hope this helps and adds to sound advice from other members. If you're still looking, I'm considering selling my black 3 door 07 GTI with 36K miles soon!
