What oil was used previously? It's possible that higher zinc can affect the copper leeching from the oil cooler.
Here's my uoa just a few hundred miles before my banjo bolt screens clogged and caused turbo failure. Copper was in the single digits although lead was elevated:
UOA by Oil Analyzers Inc. Driving conditions: Oil in use Nov. – June; 7 mile daily commute each way; a couple of days driving on the beach, no mods but spirited driving with a few WOT’s here and there. Oil changed but filter not changed. My last uoa is here . Sodium dropped nicely so it looks...
bobistheoilguy.com
I ended up keeping the banjo bolt screens in after turbo replacement because my tech convinced me that the positives outweighed the negatives. I put another 110,000 miles on the car before selling it, including adding a Cobb AccessPort at around the 110,000 mile mark, and kept my intervals at 5,000 miles.
I wouldn't worry too much about it at this point and see how another 4,000 km OCI looks. Is this a grey market Euro Forester Sti?