How to figure out kind of link and seperate / make single? I have an old blend model which is obviously made of some base parts which are used multiple times. The used parts seem to be some kind of linked objects but i can't figure out which. 

Why do i want to find out? I want to remove the bottom (green) parts here


but when i do, it removes all parts in the scene


I would like to remove this link and make all local/single. 

Also tried the  U &gt; Unlink Object+Data attempt - dosen't get better. Also exported as obj file and reimported, but links persist.

Perhaps the curved arrow icon (first image red circle) could be a hint what kind of link this is (and how to unlink).
It seems to be that you don't use the object data, for this keyboard shortcut to be useful. Then using group duplication use function Make Duplicates Real instead (Shift+Ctrl+A)