Good points neileg!
The most common radiator failure with W124 rads is the plastic inlet hose joint at the top of the radiator, which fatigues and eventually fails at around 90-150K miles of service. The resultant coolant leak is VERY noticeable. The replacement units have a metal shim reinforcement at the same joint for longer life.
The clogged radiator issue is an uncommon one for these cars, so I would agree to have tests done before springing for a $300 radiator that may not need replacing.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car