I just got back from Hamilton marine. The have newbcores sitting on the shelf for $80. I got one
I don't remember mine being that cheap a replacement.
Mine was leaking a few years ago.
I reproved it.
Found the leak at a seam.
Gave it a cleaning I'm my parts washing tank.
Sand blasted the leaking area in my blasting cabinet.
Washed with acid and soldered the leak.
Pressure tested it.
Reinstalled it and it hasent leaked in 2 years.
I did a LOT or radiator repairing growing up in my grandfathers repair shop.
These days everything is aluminum instead of copper so we replace everything.