Semantics, and you can fix a cracked blade (?) too, depending on material glue or solder or etc..... show me some images so I can check please.
I'm trying to help, you seem to be trying to avoid help while asking for help, what gives? Anyway, without checking these images we might spend another few weeks before I finally talk you into it, then once you do we see 2-3 bent pins and it was that all along.
I have seen many people look, double and triple check and see nothing "no bent pins", then show me images and I find several bent pins, or several out of alignment etc.
Testing one slot at a time is difficult on X58 due to how it is designed, if you are wanting to test slots I would first let someone else look at your CPU socket pins
Then I would follow the manufacturers layout of per module per slot, if you need to test slots 5+6 as labeled, then you must first populate the other slots per the PDF's rules.
So yes, as you mentioned, with X58 and certain slots, you cannot test until after other slots are filled. This is a given due to chipset design specifications.
Could have been dirty memory gold fingers, clean them all up with some high proof alc and cotton or paper towel then let dry for a few minutes.
Don't try to clean memory slot pins or you may catch something on them and bend out of place, unless you have very light strength long plastic fiber brush, then you can dip that in alc and clean those too if you wanted.