I mirrored the forum to be able to make searches in it, as the forum search
feature does not work at all and the search engines only find a portion of the
messages.

I always knew it wasn't state of art but after having a look at the code to
see why the mirror didn't work I realized what a huge piece of sh#t it
actually is!

It's probably not a fault of the current maintainers, and moving it would be
complex, but there's a simple thing that would at least make its mirrors work:
every page has an absurd ReadMsg javascript function that at the click of all
message links replace the link address with... exactly the same address.
While absurd it doesn't cause problems when reading the online version, but in
a mirror httrack understandably does not change the javascript, so what would
be a working link gets replaced by the function with an absolute link
(/readmsg/etc.) that of course does not work in local.
Just commenting the body of the function would make the mirror work, in effect
a current workaround is to disable javascript.