Hi Lynn
With 7.4 that rebuilder is builtin:
/forum/admin/dorebuildcontent.php?mode=forums
"Select this option if you notice something wrong with the statistics of a forum. This includes having the wrong post marked as the most recent, or if the total topics or total posts fields do not correctly denote the contents of the forum."
You can try:
REPAIR TABLE ubbt_FORUMS
in your database tools section, but it may not help much. Clear cache afterwards.