Despite how it may look, the cuts in the radiator rails are NOT a defect. They are stress relief cuts that allow the radiator to expand and contract. This prevents damage to the radiator.
As you know, metal grows when it gets hot. Then, it shrinks when it cools down. How much it grows and shrinks depends on several factors. One factor is the thickness of the material.
Because the rails are thicker than the tubes and fins, they grow and shrink at different rates. Without these relief cuts, the radiator could warp, crack, and leak.
**Please see the attached Technical Notice from Spectra Premium.**