Anyway, I started to tear down further, leaving the internal lens assembly where it is. I could remove the outer shell. Then I found the location of the loose screw. And I could also repair the copper bolt.
But next to the loose screw, one sliding path is broaken. I have put a picture in my gallery. It is in aluminium, so glue isn't possible. With dental aid I was able to fix it.
I was able to reassemble the lens and everything works, only autofocus is stiff. I assume that fixing the broken part has created more friction. It is also impossible to manualy focus. The ring slips like it does when you reatch the end of the focus.
So I need to know if the sliding path is always broaken? If not, I need to smoothen the repair of the broaken part.