Thanks for the responses about our sensitivity problem.  It looks like we
fixed it.  I dug around in the list archives some more and found post
#014259 to be very helpful.  Basically, we had a tiny misalignment of the
source.  We were able to loosen the bolts just enough to wiggle the source
back and forth (leaving the source mostly seated, with the pin and notch
lined up).  We found the extent of the wiggle and then centered the source
in between the limits.  We retightened, powered up and pumped down, and now
we're getting good signal.  It was only about a millimeter of play, but it
changed our signal by about a factor of two.

-Jamie