why not contact SOA directly and open up a case. Ask them to personally find the part and give you a date it will arrive. The information you provided in the post is lacking details regarding whether the dealership has done their due diligence. If they have gone through all the channels to get the part and it can not be found then it is not their fault. I am not sure why you think they are providing poor service (unless there are other issues).
Depending on the location and size of the leak, I might be concerned about fumes entering the cabin. Have that properly evaluated. If it is leaking in, I would have Subaru provide a loaner until they get the part and have it repaired. I would personally be all over Subaru, not the dealer. If necessary I would escalate it until they provide a date. Remind them you purchased the gold plus and expect excellent service even if they can not get the part due to extenuating circumstances.
Depending on the location and size of the leak, I might be concerned about fumes entering the cabin. Have that properly evaluated. If it is leaking in, I would have Subaru provide a loaner until they get the part and have it repaired. I would personally be all over Subaru, not the dealer. If necessary I would escalate it until they provide a date. Remind them you purchased the gold plus and expect excellent service even if they can not get the part due to extenuating circumstances.