What is best caulk used on hardie siding which was installed in 2001 in the Pacific Northwest?

James Hardie recommend using caulks that remain permanently flexible. I think GE's Silicone II, available, well, everywhere, is a good one for the purpose.

GE exuberates about its outdoor use: <q>Defy the Harsh Effects of Mother Nature: Sun-/Freeze-Proof

The outside of a home is exposed to harsh outdoor elements throughout the year. Extreme heat, the sun's UV rays, and freezing temperatures can cause acrylic caulk to lose its flexibility and degrade. The GE Silicone II* permanent flexibility keeps it from breaking down so it can protect a home as it settles or as the seasons change and joints expand and contract. This movement can cause degraded acrylic caulk to crack and crumble over time, leaving gaps for air and water to seep through. Those leaks can lead to water damage, mold growth, and higher energy bills. </q>

Anyway, good brand, good product. 5 year mold-free. I would go with that.