  Super-sonic downflows have been observed in transition region spectra above
numerous sunspots; however, little research has been conducted to date into how
persistent these signatures are within sunspots on time-scales longer than a
few hours. Here, we analyse the lead sunspot of AR 12526 to infer the
properties and evolution of super-sonic downflows occurring within it. Sixteen
large, dense raster scans sampled by IRIS are analysed. These rasters tracked
the lead sunspot of AR 12526 at discrete times between the 27th March 2016 and
the 2nd April 2016. One sit-and-stare observation acquired on the 1st April
2016 is also studied in order to analyse the evolution of super-sonic downflows
on shorter time-scales. Super-sonic downflows are variable within this sunspot
both in terms of spatial structuring and velocities. 13 of the 16 raster scans
display some evidence of super-sonic downflows in the Si IV 1394 {\AA} line
co-spatial to a sustained bright structure detected in the 1400 {\AA} slit-jaw
imaging channel, with a peak velocity of 112 km s^{-1} being recorded on the
29th March 2016. Evidence for super-sonic downflows in the O IV 1401 {\AA} line
was found in 14 of these rasters, with the spatial structuring differing from
that inferred from the Si IV 1394 {\AA} line. In the sit-and-stare data, no
dual flow is initially detected, however, a super-sonic downflow does develop
after 60 minutes. This downflow accelerates from 73 km s^{-1} to close to 80 km
s^{-1} in both the Si IV 1394 {\AA} and O IV 1401 {\AA} lines over the course
of 20 minutes before the end of the observation. The morphology of these
downflows evolved over the course of both hours and days and was often
different in the Si IV 1394 {\AA} and O IV 1401 {\AA} lines. These events were
found co-spatial to a bright region in the core of the Si IV 1394 {\AA} line
which appeared to form at the foot-points of coronal fan loops.
