re=core or new radiator for my 81?
 

My 81 has developed a leak around the top plastic. I actually think it's been there for some time, as the coolant level is always a couple inches low, even when I first bought it. It was not until I cleaned everything up, and added a new cap that I even noticed it, but if you fill it full, it will leak back down when your driving it. I've had it parked since finding it.

Should I buy a new radiator or just have the original recored?

Well a new one will cost you plenty. Your description of the problem is rather ambiguous, but if it has a small leak between the top tank and core, I would certainly try to repair it with JB weld. Give the JB ample time to harden, at least 12 hours, or if you can 24 hours. That would be my solution if the car was an average 81 300-D and my daily driver.

Good looking junkyard radiator might be a more reliable option then attempted repair. Because of their age a lot might have replacement rads in them.

i had a 560sl aluminum rad cleaned and re-tanked for $150.00. Hit me up... the guy is in fort payne and is very reasonable (or was, at least, in my case). The hose neck had broken off. He replaced the tanks and cleaned and returned to me in "like-new" condition. I still have it boxed up, just in case...