How to fix corrupt comments file?

Hello,

My site was hacked by comment spammers:

https://www.electronicrecylcingofmt.com

I’ve repaired some by upgrading to 3.3, and now I am actively removing all the comment spam through akismet. But something was still not working. From an expert examining the 404 logs, I’ve been told that I need to replace wp-comments-post.php, it is corrupt. I think that I can do this by ftp. But I am not sure where to get a clean version of this file. I thought I could find it in theme itself. But when I download it and and unzip all it has is a comments.php and a commments-popup.php.

Any advice to fix this will be greatly appreciated.