I think the trick to buying anything with a brand new engine is to run it for a short period of time and then drop the oil, change the filter and do it again within the next 6 months. This way you may be lucky enough to have caught some metal shavings, etc in the filter and oil and been able to remove any potential future problems.

With the Micra the oil filter is so small I wonder if it does anything at all to catch impurities. Even my whole house generator and lawn tractor has a larger filter than my Micra.