Here's how I look at it:
Considering Nissan has now sold about 28,000 Micras in Canada, and we've only heard of a handful of owners getting engine warranty work, it's far from a common problem.
Also consider the exact same engine, from the exact same factory, is used in the Versa Note. You can check the Versa forum as well. (Half the posts about the issue there are from the same disgruntled South American owner who posted here.)
Second lastly: the "test" for checking for bearing issues is pretty simple. (It's laid out in that thread.) So if the used Micra you're interested in doesn't make any odd sounds when you slowly increase the RPM in Park, I personally wouldn't worry about it.
Finally: it's warrantied for 5 years/100k kms. If it doesn't show up before then, it's probably not going to show up.
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View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...