I thought they usually last up to at least 70 or 80,000 miles? WTF? Going to do have the shop do thermostat too now, since I'm at it.

I wonder if it has anything to do with being Cobb tuned for the past 3.5 years / 30,000 miles... I know some tunes, like the Dinan flash, turn up the water pump's speed to assist in cooling, and perhaps that leads to premature deaths on these things?

Here's Dinan's quote:

Remapped Water Pump Speeds To Control Engine Temperatures
The N54 engine is known to run a little warm in stock form. In an effort to more effectively control oil and water temperatures, the Dinan software actually increases water pump speeds as boost pressure increases.

Dinan Stage 3 Performance Engine Software/Boost Upgrade for BMW E89 Z4 sDrive35i - Dinan, Leader in BMW Performance Parts and Upgrades
.
.
.
Anyone know if Cobb does it too? Though you wonder how much impact it would have even if it did, since it's supposed to be only with increased boost, and with city driving, it's not like you're in 15 PSI of boost all the time...