Found an older thread by Cookeh:
Heater core ...see post #13 from SwedishBus who reckons, at the time, the
PFS supplied part is better made than the original as it has brazed cooling fins.
There is also a
42mm and
48mm MAHLE core available from Auto-Doc, the 48mm producing higher output, but I can't see a 48mm with brazed cooling fins.