I ordered a 15t from them for the 04 but they just called and all they carry is the 13t and 14t for the '04.
Will I need a new chain if I go with the 14t or should I just order a 15t for a '02 model?

Thankyou

Nevermind, it's only $20 and I'll go ahead and get the 14t.  I'll get a 15t from somewhere's else and feel the difference.

Sprocket Specialists were confused, because they think the stock sprocket on the GS is a 15t.  One of the techs said.

Check the last 10 or so posts on this thread...

http://gstwins.com/forum/viewtopic.php?t=13703

Sprocket Specialists won't start production of a 15T for the 2004 GS500F until later this spring.

You can get a JT Sprockets 516.15 now though that should fit.