If you haven't had the home inspected yet, do so, and use an ASHI-approved inspector. Make sure you get an inspector that will give you a report on the spot. You don't want to have to wait days for the report because if you have questions, it's best if you're all at the house when you ask them.
The inspector usually gives an approximation on the age of the furnace and how long it might last. Oil forced-air is not bad in and of itself. There are other issues related to it like, is the tank buried underground or is it above ground? Removal or maintenance to fix a leak is costly from what I hear. In the meantime, I'll check with 'my best man' who runs an oil and gas furnace company in MA about this and get back to ya.