You're correct on the service life of the BMW radiator. Def a weak point.
I've been looking at them as well.
They are quite a few Radiators out there.
OEM style but all alum
https://www.turnermotorsport.com/p-1...l-cooler-tabs/
Fluidyne 44mm
https://www.turnermotorsport.com/p-1...6-323325328m3/
And PWR makes a 55mm (PN 20-03109)
https://www.crracing.com/products/ca.../bmw_radiators
C&R Racing 20-03109: OE Fit Aluminum Radiator BMW E36 | JEGS