Allow me to help.
The text file says to find...
$this -> ubbt_setcookie("{$config['COOKIE_PREFIX']}ubbt_dob","",time()-3600);This is VERY close to what is in the file html.inc.php.
On or about line 1448, you will find...
$this->ubbt_setcookie("{$config['COOKIE_PREFIX']}ubbt_dob","",time()-3600);Note the lack of space characters in the string "$this->ubbt".
When doing Mods, you need to be willing to look a little harder.
I did as you apparently did and searched for the whole string from the text file. When that did not find a match, I started doing a search for "ubbt_setcookie" and found what was needed.
I have this Mod working fine.
Remember for 7.3x you are looking in "html.inc.php".
