Prestone Coolant Flush Kit Okay?

[Abner Mality]

The vehicle is a 1990 420SEL with just over 170K miles. I want to flush the coolant, but do not want to take a chance on screwing up with the citric cleaner. Is the Prestone backflush kit okay to use on these cars? Would the typical splicing into the heater hose be the prescribed method? Any help or advice would be appreciated. Would especially like to hear from owners who have had success with the Prestone or other backflush kit. Thanks in advance.