Apache always logs 403s, thats built in. Are you sure apache isn't logging these 403s?
If apache isnt logging 403s, then either this isnt being generated by your server, or your system is totally hosed.
I'd double check your logs. If you dont see apache logging a 403, and its sending something else but your user is getting a 403, then its not coming from apache, modsecurity or ASL - something else is doing it - or if apache is sending a 403 and not logging it, your system is, as previously mentioned totally and hopelessly hosed. Time to reinstall, thats a critical massive error or major misconfiguration.
So please let us know what apaches logs show you, if your system is doing this its got to be logging it. Check your error logs and audit log.