Hi Alex, Congrats on the car! Sounds like a nice one too!
The radiator is a 'known issue' and I would say we all end up replacing them at some point. I had mine done representatively when fixing something else that involved removing the front clam.
I went with this one from Elise parts https://www.eliseparts.com/shop/engine-br-gearbox/cooling/aluminium-upgraded-radiator/ check it fits your car first (the site shows model compatibility).
But there is a cheaper aluminium one on there which will probably do the job perfectly also. The upgraded one runs my car 1-2 degrees cooler but