I have a 2009 Dahon Speed TR and live in a high humidity coastal area with tends to rapidly corrode unprotected low quality metal. I ride around 4000 miles per year. I have had no issues with the Dahon hinge. I have not lubricated the hinge since I bought it. I have adjusted the tension, once.

Like you, I purchased my bike second hand.

I hope your hinge issue is not serious and is just a simple need of lubrication and adjustment.