Thank you - your guide worked fine for me! :)
The left-click of my heavy-used trackpad didn’t work anymore but now it’s back in business. The art is to use force in the beginning when slicing through the adhesive in the first corner. And then you have to be patient when working down and in - centimeter for centimeter… ;)
what iFixit doesn't phrase clearly is the fact that there are 2 hdd configuration types. There are a number of Mac Minis shipped with HDD in UPPER position (as shown as in Mac OS X). Almost every upgrade guide on the internet (incl. ifixit) doesn't even mention the possibility that these costly upgrade kits won't fit in your Mac!
Unfortunately iFixit doesn't offer this particular cable for the LOWER slot (076-1412). The cable 076-1413 for the upper slot does not fit for these Mac Minis with HDDs shipped in upper position.
Spent money for nothing... :(