i actually had this same issue a few days ago. grc reported everything stealth except 1024.

zonealarm just wouldnt block the port.

solution to the issue, download kerio firewall. http://www.kerio.com/kpf_download.html

this firewall blocks everything grc.com can throw at it. even port 1024. its easy to use and just like everything else, it learns your system. you give permissions for your programs.

my fax service uses port 1024, kerio permits usage but leaves the port stealth.