I would try something like:
Code:
\n\n\d{1,}\n\n.*[a-z]\n\n
Which is two newlines, + one or more digits, + 2 more newlines, + a string ending on a lowercase letter, + two newlines. It'll take some wrangling to rework that into Word's "regex," but if you rip it into something else that ought to work directly. Take care though if any of those headers end on anything other than a lowercase letter (trailing whitespace, punctuation mark, etc.).