Some months ago there was a ebay seller in my country with a 100% made from copper core which nobody bought, fully copper core's are rare, I should have bought it.
I believe the plastic top & bottom core's are the same from the Sprint and late 33's. The only difference in there efficiency is the series3 33 has a stronger blower. I don't think there's anything wrong with an original core as long as people use quality coolant and change it every one or two years.
Unfortunately to many people never change it or use tap water then wonder why there heater stopped working and just think the core is crap.
I say take your core out get it repaired or a new one, use quality coolant changing it every year and earth the fan blower directly to the battery.