Whereabouts in Sydney are you?
I have a few spares here & a brand new radiator that you're welcome to temporarily use if it helps get to the bottom of the problem.
I also think having a 2nd hand radiator 'reconditioned' is a bit odd for a workshop like Davis' to do. A new genuine radiator would be my preferred option, or at least a new Chinese one which are less than $200 these days.
Just my opinion though, I'm sure Bruce & the team know what they're doing.

