The "fix" depends upon your geographical area. Where I live in California, the radiator shops don't repair the plastic tanks. Call some of your local shops and ask them if they do, and if they use Accutech epoxy to do the job. There is a company called "North East Plastic Tanks" in Farmingdale, NY that sells replacements. 800-300-7539, or email: NEPlasticTanks@aol.com
They may be able to recommend someone in your area they sell to.
Then, you should remove the upper hose, and inspect the hose connection to the radiator to assure that it hasn't broken. This is common on the plastic tank radiators, and usually requires a replacement, but again, if you can get it repaired, it's cheaper.
If you replace it, make sure the new one has the brass insert sleeve in the upper hose connection "neck". Some new radiators are made with these to prevent future breakage, but not all are.
PartsShop/FastLane will have your radiator, either a Behr, or a Nissens. Check it out...