1989 Mercury V200 Power Packs

[BuilderFL]

I have been having problems with the power packs (switch boxes) and although I’ve heard that you should replace both if one goes, I have only replaced the one that goes bad (they are about $170 ea.). But it’s happened over three times in less than a year. Is there any truth reasoning that they both need to be replaced if only one goes? Should I be looking at other ignition components that may be causing the early failure of the power packs? As always, your help is appreciated.