It’s been very interesting to read all the comments on cracking. I too have been afflicted with cracked Lego.  

I create a few MOCs once in a while, but mostly keep sets intact in Sterilite bins in a temperature controlled closet. I live in Utah (a dry area) in the US. I allow my children to gently play with my Lego after they have washed their hands.  I never take the arms or hands off. 

I have found 163 pieces with a crack or break out of about 55,000 pieces.  39 of the 629 minifigures I own have had cracking issues.  That’s 0.3% of the entire collection, and 6.2% for minifigures.  For me, it has been across all themes. Though I have noticed that some sets have more issues than others, such as 7965 Millennium Falcon. Could this be related to where the set was produced, shipping conditions, or storing conditions even before the set was opened? 

It is interesting to look at the issue from different angles: the Lego group, kids, and AFOLs (or should it be AFsOL?).  From a corporate perspective, 0.3% seems like a pretty good rate, statistically speaking; however, 6.2% is not nearly as good... But I only have my own data to go from. My kids aren’t really bothered by cracks unless it affects the functionality of the piece or is very noticeable.  For me personally, cracks in a valuable or cherished minifigure is very irksome.  

Based on the discussion so far, it seems that there are several factors that could be contributing to cracking:  

1.       Fundamental quality –  weaknesses in the plastic, molding etc.  

2.       Environmental conditions – Humidity, temperature, sunlight, etc.

3.       Play – How the pieces are handled, stressed, hand oils, etc.

4.       Time – cracks appear even though pieces were not touched or used

As others have said, it would be very difficult to pin down the exact cause, as everyone’s circumstances are different.  More than likely there are multiple factors combined that contribute to cracking. Though it would still be a relatively small dataset, it would be great to get more feedback from others in the forum on these correlating factors to see if there are any patterns.

With more adult fans (highly scrutinizing of quality) buying more Lego than ever, it seems an issue that cannot be ignored by the Lego Group.  As others have mentioned, Lego has fantastic customer service in this regard. But it is certainly frustrating when a piece cracks after a very short time or is no longer available to be replaced.  

I've noticed new figures are prone to cracking, as for older Minifigs...... when they crack, they seem to crack mostly in the arms.