I have an arbor-mounted R8 drill chuck (Rohm keyless, nice chuck) for
my Excello vertical mill. A while ago I came in one day and found
that it was running ~10 thou out, probably because someone
accidentally cranked the vise into the side. I asked a couple of
professional machinists and they told me to simply find the high spot
and use the side of the vise to simply press it back. I tried it and
it worked fine, although I ended up buying a new Jacobs ball-bearing
Super Chuck for $40 and a new arbor. The old arbor, which was quite
dinged-up, went into the scrap bin, while the Rohm keyless got a new
MT2 arbor and was dedicated to lathe use. After measuring the TIR of
the old chuck and arbor separately, I'm pretty sure that the runout
was in the taper connection, and not an actual bending of either of
the parts.