Down at the bottom of the page it has dowload tech manual. I downloaded on e for mine. It has an exploded view of the fork. In the 2000 models there are 4 Z 1's. You can also get a whole lot of great information form their web site. Ok I went to the site and looked at a view of a ZI CR the manual does not show the cartridge as being able to come apart like that. I would pull the cartridge hold it by hand and try to thread it back in. You may want to seriously consider replacing that part!
I would replace it, but the rep for my area tells me that they have run out of catridges in australia. This means it would have be ordered from Italy, so it would take ages and ages to get here. Plus its $200 for 1 new catridge.
Marazocchi dont seem to consider the catridge a servicable part. I had a look at the manual on the website and the whole catridge is a single piece in the exploded view. Also, the rep didn't know anything about putting it back together.