used Redline MT 90 in my 2001 jetta O2J 5 speed samo in my TT O6M 6 spd great stuff + since its not just tranny lube in FWD it sees harder use + shorter life. Redline is better than OE in my bought new jetta as well as my lo mile preowned 2001 TT that was shifting poorly until i changed it.
Since 75W-90 is more than twice as thick as what's been in there, I'd almost bet you'll notice stiff shifting next winter. Hope it's just marginally stiffer in the morning.
But more important, did you ask your dealer what's been factory fill? Perhaps G 052 527 like what the 02Q six-speed use? Hard to assess this UOA without knowing what sort of oil it is. It's just a vast amount of iron and some copper.
On a side note, I've been a strong advocate for early gear oil changes for quite some time. I use to do this on any new car at just 2000-3000 mls. Since no gearbox/transmission leaves the factory as clean as most would think and there's some elevated emergence of iron and copper due to run-in this is the most important gear oil change of all. With normal use on most cars you're fine with 30,000-40,000 OCIs later on.