I figured it out, so I thought I'd record my solution here if anyone else is looking for it.
The problem is (besides the obvious typo '[' should be '[') is that I need to be looking for BOTH \r and \n for the boundaries. That's why I could never find more than 1 \n in a row.
...blah blah blah.\r\n
\r\n
MATCH THIS TEXT.\r\n
\r\n
Blah blah blah...
so the correct regex should be:
/\r\n\r\n[.]+\r\n\r\n/sm