The move from webwork.maa.org/moodle to wwrk.maa.org/moodle may be the prime reason that some explicit cross-references in Forum posting are broken. However, there are further difficulties involving internal numerical IDs for postings, e.g., the two links in Davide's note at http://wwrk.maa.org/moodle/mod/forum/discuss.php?d=359 do not succeed even after "webwork" is revised to "wwrk".
In the near term, the work-around would seem to be
1) try the simple search box (in upper-right), but expect it to fail
2) use the subsequent advanced search page and scan its output
[T]he two links in Davide's note at http://wwrk.maa.org/moodle/mod/forum/discuss.php?d=359 do not succeed even after "webwork" is revised to "wwrk".
Are you sure? I am successfully sent to the appropriate pages upon clicking them (no substitution necessary), although that might be due to someone changing things over the weekend.