The litmus test for reserve alkylinity is only valid for conventional "green" antifreeze, so they are not valid for pure organic formulations such as Dexcool, or hybrids like MB brand or Zerex G-05, which is the same formulation as MB brand and approved for all DC vehicles.

Your best bet for coolant system longevity is to replace the antifreeze at the manufacturer's recommended change interval, which is every three years, regardless of mileage, for MBs.

Duke