Agree on Fujitsu thermal spec's.
Mean-Time Between Failure (MTBF) specs are always "characterized" at some temp. point, which is typically 18°C. Each degree-per-period of operation above this characterization point (or outside of the gradient/h) [continuously] knocks thousands of hours off the MTBF.
Non-climate controlled (i.e. non data centre) inside-case temps are usually way above 18°C. This is why active air-flow helps reliability.
Fujitsu's are (or were the last time I looked) characterized at a far more realistic 24°C (exclusive of 15,000RPM drives).
/S