Classic industries radiator finally gave out

only when running water (for racing)
All coolants have anti-corrosion packages in them.
The different colors denote the different corrosion inhibitor packages - well they are supposed to.

Conventional green indicates inorganic inhibitors that are effective immediately and so are well suited for open and partially open systems.

If yours is copper, then it should be fixable. Might be as simple as a poorly soldered seam. If its pin holes in the core tubes, that can be patched for now. That will give you time to find a good one.