LEGO bricks getting brittle, easily breaking. Insight needed
For whatever reason, several Lego sets from 2008 are known to have had this issue. The trouble seems to be part specific. For example, the Lego Bionicle Karda Nui set 8686 Lewa Nuva that contained four Technic Beam 5 with Two Ball Sockets in FabuLime (Lego part number 4539223) often cracked upon initial assembly or disassembly. Replacement parts obtained directly from Lego exhibited the same issue. 

Because of the consistent high quality of Lego manufacturing, on the rare occasion that we find a bad part, we tend to blame ourselves for the part failure. Logically, if the trouble is exhibited across the entire set (example: brittle parts) then it is probably safe to assume environmental issues like exposure to sunlight or temperature extremes. However, if the problem is only exhibited in a single piece handled with proper care, it is reasonable to assume manufacturing issues. 

In my experience, Lego warranty part replacement services will never admit to or discuss known issues with Lego sets or parts. It must be against company policy. However, much to their credit, they will replace any part they have in inventory, no questions asked. So, if you have an issue like this again, contact them immediately. The catch is 'parts they have in inventory'. For older sets they might not have your part, so you would have to use a service like BrickLink.

I have thousands of Lego sets. Rarely, I have found a malformed or missing piece. The odd brittle piece problem seems to be confined to several 2008 sets. Maybe Lego was experimenting with new pigments, ABS formulations, or manufacturing processes that year?