would not suggest to repair the radiator. yes it solves the issue in the short term, but over time, the welding, or the repaired part, might weaken and expose another risk. same goes to the used radiator, as u wouldnt know the mileage it has gone thru, and if there are issues/clogs in them. for used, its just a matter of time before u need to change it again.
A new one, be it original or OEM, at least gives u piece of mind. OEM would work just fine, and perhaps u shld take it as part of ur preventive maintenance program.
my 2sen la....