@Bash64:
Viton o rings can be found on ebay. See here:
http://www.ebay.it/itm/IMPERIAL-SIZE-VITON-RUBBER-O-RINGS-CROSS-SECTION-1-78MM-SIZES-BS004-BS033-/221138552287?pt=LH_DefaultDomain_3&var&hash=item337ce285df&_uhb=1
This seller seems to have a very good set of those rubber o rings. According to what I've read a dual 2.7 G5 has a Viton with those specs:
Viton AS568313A Aerospace Standard ID Number: 027."
Number: 027." Dimensions: ID = 1.313", OD = 1.438", thickness = 1/16"
The seller specifies dimensions in centimeters so I did a little conversion and:
1.313" = 3.33502 cm
1.438" = 3.65252 cm
So if you select the BS027 you will notice dimensions are in the range. Of course, you have to check your Viton o rings to be sure you are not buying something else (I'm not really sure o rings are all the same dimensions changing G5 model so better be careful and search about before!).
About Cooler MAster coolant liquid that kind of uv blue liquid is discontinued and out of stock (as you've seen). I don't think that another liquid couldn't be used provided that it is a non conductive liquid. So distilled water would be enough. If you want to take a look to Feser One that is described as a really good product:
http://www.amazon.com/computers-accessories/dp/B000P0OU0Q