Suicidal apache

[ephigenie]

but you're using fastcgi aren't you ? because then memory leaks of php normaly do not affect apache (except you got OOM Messages and your apache got killed by the kernel)

Otherwise you can enable a php-log for the domain you guessed the script is on.
Just go to your /var/www/fcgi/<domain>/<phpVersion>/php.ini

Perhaps you can even try to use a different php version for that host...