My 2 cents.
Obviously wait to see what SOA says. I am not sure how a Subaru warranty works when there is an intervening private sale. I suggest you read the warranty manual carefully to see if a private sale has any effect on the warranty. I suspect not, but just make sure to nail that down as you begin to "get your ducks in a row."
If SOA tells Patriot not to fix, then your beef is not with Patriot, but with SOA. IMHO the first step is to get the history on the car. Car Exeter Subaru and get as much information as you can. Find out what "goodwill" service means, etc.. When you call, ask who you are speaking with so you have their name. Explain your situation politely, and ask for a copy of service records. You may have to show you own the car--maybe Patriot can help you get this information, but it is important for you to know exactly what happened here so there are no surprises later.
You asked for the person's name at Exeter Subaru because you may want to confirm that, and any other, conversation in writing depending on what was said--use your judgment. When you have all information, and you believe the warranty should still apply, it is time to call SOA customer service and plead your case. Again, get the person's name and followup with a letter confirming the conversation--every time. I suggest you spend some time writing the letter to SOA, then use it as an outline for the phone call.
You might even consider calling SOA now, while the case is under review to plead your case a bit and at least ask them what the process is to contest a warranty decision should it be unfavorable. Ask the person's name and for them to send you in writing the process and any other information you want. Again, confirm with a letter (they may also reference calls by a contact number--ask if they do and reference that in the letter as well). Always be polite, do not lose your cool, be firm and professional. It may take more than one letter or call, but eventually you may wear them down.
Lastly, send the knee-cappers to the person you bought the car from, and who did not disclose this information :- I presume the bill of sale says "AS IS" or something of that nature?
Good luck.
Brett