Before you deem the turbo charger failed. Have the oil lines supply and return checked to see if they are not leaking themselves.
I don’t believe the banjo bolt applies to the Forester XT engine. It is exclusive (unfortunately) to my 2005/2006 Legacy GT and 2005/2006 Outback XT only.
$2000 seems very steep especially for a non-dealer for a turbo replacement. Get a 2nd opinion. Do you leave in the Boston or New Hampshire area? I can recommend some good shops for Subaru.