Thanks for all the input. Just updating that I've opened a case number
with Sun and they've sent me a newer model chassis fan and
fan/heatsinks. I haven't had time to install them yet.

The new F310-0020 part is shown in the revised Sun Java Workstation
W1100z and W2100z user guide, 817-6585-12.pdf (downloadable from Sun).
The fan is mounted on top of the heat sink now, rather than the side.