Welcome to MyFico Forums, and really glad to hear things are going much better for you. Hope you enjoy Happy Holidays!
First things first: How do you know you still owe $7800 on it? That sounds like a very high amount considering you apparently bought the 2009 car in 2012 and made payments on it for 5 years. If the balance is really that high then Capital One likely bumped up the balance with late fees, other fees, and a very high default interest rate. And the obvious reason they haven't tried to repossess the car is that as you've moved so much they have no idea where to find you. But even so it is highly unlikely they would try to repo on a loan in default for over 3 years with no payments, and for a car worth less than half they balance owed, even if they could find you.
Have you gotten an estimate to get the oil leak fixed? Subarus have very good reputations, and 114k miles is not that much, especially for an 11 year old car. If it can be fixed for a reasonable amount your best bet is to just keep it. Are you planning on applying for new credit? If not, 3-4 years it will be off your credit report, and the Capital One loan will only be a problem if you try to sell it. If you really want to get rid of this you might see if they will settle for $3k-3500, as I said that balance has to be bumped way up with fees & default interest.
But since you've enjoyed several years of peace & quiet, contact them in a way they can't bother you if you can't reach an settlement they can't start harassing you with collection calls. Such as get a free Google Voice phone # you can get rid of if it becomes a problem. But, while there are many lenders who will follow you to the ends of the earth to get how ever much money they can get out of you, Capital One isn't one of them, they're usually fairly reasonable.
All the best to you! 