Does anyone know if a 2004 rear axle will fit a 2007. I thinking  its the same I just want to make sure before I order it. Thanks.

I'm pretty sure it probably is. I know the 89 is a 17mm diameter, I'm 99% certain the axle size is exactly the same, since you can fairly easily install the katana 600 wheel to these bikes without much modifying, and they also use a 17mm ID bearing.      Oddly, my 87 Hurricane600 uses the same axle size, which I actually find kind of funny. means I could PROBABLY do the kat 600 rear wheel swap on my CBR.

Same part number for 04 and 07 GS rear axles,  they're probably all the same.  Your parts fiche is your friend in checking interchangeable and superceeded parts.  Just takes a minute to check.

http://www.bbburma.net/Documents/GS500_Parts_Fiche_1.html