It's more expensive initially, but just replace the radiator. Both th upper and lower tanks are plastic, and there are more cracks than you know of. I had a '96 Celica GT, and thought I only had one small leak. When I pressure tested the thing, I discovered the entire tank was cracked. Same issue happened on may Camry and my friends '91 Celica.
I took mine in to a radiator shop and had the radiator replaced for somewhere around $110 I think.
