Hi Laurent - the current OSX beta has the lwo contour stuff in it. You need to enable it though by editing moi.ini - to do that go to Options > General and push the "Edit .ini file" button.

The .ini file will open up in TextEdit.app .

Then go to the [LWO] section, and edit the WritePartTags=n entry to be =y instead, like:

[LWO]
WritePartTags=y


That will then enable writing the part tag data to the LWO file. Then to enable contour rendering there are a few steps you have to do in Modo to set it up, see this previous thread for instructions:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3926.11

- Michael