If your Go board is indeed a 2004 model, you do not have the "Toughskin" construction.
Year model 2004 Go/Start/Free Formula boards were N-ASA construction.
Here's the link to the 2004 "Technology" site:
Scroll down until you find the N-ASA construction.
This was the precursor to "Toughskin", but the Toughskin is heavier and uses a thicker
ASA layer molded on the out side.
You should be able to repair N-ASA construction using simple easy to obtain epoxy resins, fillers and fiberglass cloth.
If it's just a cosmetic "scratch" in the ASA (or even through the ASA to the first glass layer) just fill it in with a product like Marine Tex and then give it a coat of paint to stop the UV yellowing of the Marine Tex filler.
Hope this helps,