This mod finally fixes the Liberty City Stadium gates. This may be exactly the fix you've been looking for for years. Now the stadium will work as intended.
Installation:
Simple way: Move the Stadium Gate Fix folder to the GTA 3 Modloader directory.
Traditional way: Use IMG Tool to replace the files manually (don't forget to back up the original files).
Compatibility: The mod works in both the original version of the game and in modified builds such as Updated Classic and Classic Edition.