The S52 M3 cooling system fails in the same plastic-heavy order as any E36, and it takes M3s out the same way:
- The radiator's plastic end-tanks go brittle and crack.
- The water pump's plastic impeller erodes or its shaft fails.
- The expansion tank, its cap and the thermostat housing crack or leak.
I do them as a package, not one at a time.
For a tracked M3, I add a larger all-aluminium radiator, make sure the viscous fan clutch and auxiliary fan actually work, and consider an oil cooler — sustained track load is where a marginal system boils over. And I fit a metal-impeller water pump.
For the refresh you'll want the radiator, a metal-impeller water pump, the expansion tank, cap and thermostat/housing — I've put them below.