I just picked up a "rebuilt" water pump of unknown origin on Ebay.  I
am gearing up for a timing belt inspection and am going into it
planning on needing to replace that belt.  I have read several places
that one should proactively replace their water pump during that
exercise.

My questions:
1) How do I know that the "rebuilt" water pump is any good.  It is
fairly shinny and clean enough to make it plausable that it was
rebuilt, then spent the last few years sitting on a shelf in a garage.
2) The part number stamped on it is 944 106 122 6R - I don't find this
number in any of my searches, although there is a picture of a water
pump that is identicle to this one at the germanpartsonline web site,
and in that picture it appears to have the same number stamped on it,
although the one and the 6 before the are a fuzzy so I may be
projecting that one.  That picture can be found under BOTH early AND
late model NA 944s (both manual and automatic), but there are also
pictures of a different model and it is not clear how accurate their
site is.  Searching for that part number (less the 6R) returned no
hits.
3) Am I being silly with my plan to replace a part that I know is
currently good (and spend another 40$ in the process buying a
gasket/thermostat/new bolts)?
4) How freely should the pump portion spin? This one seems to have
resistance, although does turn w/o noise or detectable wobble of any
sort.
Thanks for your advice!