  We have monitored the massive binary star $\eta$ Carinae with the CTIO/SMARTS
1.5~m telescope and CHIRON spectrograph from the previous apastron passage of
the system through the recent 2014.6 periastron passage. Our monitoring has
resulted in a large, homogeneous data set with an unprecedented time-sampling,
spectral resolving power, and signal-to-noise. This allowed us to investigate
temporal variability previously unexplored in the system and discover a
kinematic structure in the P Cygni absorption troughs of neutral helium wind
lines. The features observed occurred prior to the periastron passage and are
seen as we look through the trailing arm of the wind-wind collision shock cone.
We show that the bulk of the variability is repeatable across the last five
periastron passages, and that the absorption occurs in the inner 230 AU of the
system. In addition, we found an additional, high-velocity absorption component
super-imposed on the P Cygni absorption troughs that has been previously
un-observed in these lines, but which bears resemblance to the observations of
the He~I $\lambda$10830 \AA\ feature across previous cycles. Through a
comparison of the current smoothed particle hydrodynamical simulations, we show
that the observed variations are likely caused by instabilities in the
wind-wind collision region in our line-of-sight, coupled with stochastic
variability related to clumping in the winds.
