There's always an expert at every garage that knows better than the people who make them...

Good luck, hope the oil change sorts it, I managed to get many 0000's of miles out of mine before the inevitable...  Pete
I now have permission from the boss to use Y.O.L.O. Enjoy life
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Your fluid and magnets did look well OK.

Most certainly a no for mineral fluid.

I totally agree with the required spec for the fluid that is required (LT71141) However I also believe that alternatives are available.
Some alternatives are actually cherry red not the Tan colour that is expected with the OEM fluid.
If you are to source alternate fluids do your home work.
I have been using a cherry red fluid for 2 years+ with no detrimental effects all I have seen felt and heard are improvements, I know this is in opposition to what is reported by some members and I have no qualms about their advice at all, it is mostly correct.
You could possibly have had an alternate fluid and not a very well repaired trans.
Possibly it has Dexron 3 in it, its hard to know unless you talk to those that did the rebuild.

Get out and see a few Auto trans specialists......if you have the time. As Haylands says there are some that think they are Gurus and are actually phoneys.
RR Phil is the authority on this forum for sure and all he says makes plenty of sense.

Research and canvasing good workshops that have experience with the FF is what you need.

OEM fluid is very expensive, its a good way for a workshop to make some extra profit by substituting with a cheaper substandard fluid.
Find a ZF authorised workshop if you are cashed up.