You're correct, it is the OEM plastic tanked one. I checked the hoses and they seem ok, checked top while running and couldn't see any obvious leak under pressure.
I ended up getting a brand new off Trademe, just a plastic one still for like $160 shipped so will see if that solves the issue.
Although, a friend told me his did this and it was the hard line across the top of the rad to the overflow was blocked and was forcing it back out and leaking. Need to check that too.
Early BL, 2003 sedan, Spec-B, think it's a PFL, but top spec PFL... Or FL of the earlier gen.