I run a Radtec in the crossflow and when I asked them what antifreeze to use they recommended Bluecol. They said they had a qualified chemist working with them (I think as a consukltant) and that was his recommendation. But as you say Jonathan, the engine may dictate what to use. Maybe ask Radtec about both the repair and what antifreeze to use - certainly they were very helpful when I spoke to them. If they do repair it, they may also be able to tell you why it might have failed. Good luck sorting it!