  We present the results from a monitoring campaign made with the Neil Gehrels
Swift Observatory of the M51 galaxies, which contain several variable
ultraluminous X-ray sources (ULXs). The ongoing campaign started in May 2018,
and we report here on $\sim1.5$ years of observations. The campaign, which
consists of 105 observations, has a typical cadence of 3--6 days, and has the
goal of determining the long-term X-ray variability of the ULXs. Two of the
most variable sources were ULX7 and ULX8, both of which are known to be powered
by neutron stars that are exceeding their isotropic Eddington luminosities by
factors of up to 100. This is further evidence that neutron star powered ULXs
are the most variable. Our two main results are, first, that ULX7 exhibits a
periodic flux modulation with a period of 38 days varying over a magnitude and
a half in flux from peak to trough. Since the orbital period of the system is
known to be 2 days, the modulation is super-orbital, which is a near-ubiquitous
property of ULX pulsars. Secondly we identify a new transient ULX, M51 XT-1,
the onset of which occurred during our campaign, reaching a peak luminosity of
$\sim10^{40}$ erg s$^{-1}$, before gradually fading over the next $\sim200$
days until it slipped below the detection limit of our observations. Combined
with the high-quality Swift/XRT lightcurve of the transient, serendipitous
observations made with Chandra and XMM-Newton provide insights into the onset
and evolution of a likely super-Eddington event.
