Nothing wrong with a used transmission. Just pull the dipstick before you buy. If the fluid is a real bright red, you should be good. If it's a very dark maroon I would pass. Brown and the tranny is already on it's way out.

 

Damn good info Dave as always. I would like to ad that when
going with a used unit that checks good as you suggested. I would want to
do a fluid change or flush once it was in as well as a filter change. So ya
drop the pan and see how much metal and friction crap is in it. Than make
damn sure you know what fluid was used in the replacement tranny so as to
be sure and replace it with the same ATF. There are different ATF's that are
used in a C6 over the years and if ya put in a different one than it was broke
in and ran with it wont last at all.

On another note the master over haul kit is not all that much and
comes with very good instructions. At least the Fram kits I used back
in the 80's and 90's did. At the time the Master was under a $100. Don't
know now. If you can follow the instructions on building a model car
or plane. Or have done any thing like this you can over haul a C6.
Just get it super clean and soak the clutch disks over night at least before
re assembly. The guys here as well as I would walk you through it as well.
Bud you can do this and it could be fun. Stick a used tranny in it while
you try your had at a rebuild. If the used one seems to be working out
than sell your rebuild one and recover the cost and more. It's a win win
thing my friend.