I'm a devotee of regular oil and filter changes. 20,000-mile service intervals are clearly aimed at fleet operators keeping maintenance costs down and are irrelevant to many of us. I bought my 1.2-litre Corsa SXi new in March 2004 and have changed the oil and filter every 10,000 miles since then (roughly every six months). I also used Shell V-Power from day one and so far have racked up 165,000 miles. The car is still on the original camchain and tensioners. Keep the oil and engine clean and it will look after you in the long run.