"I have purchased 6 new LEGACY engines (American Flyer) and five had board failures and went back to Lionel for repairs."
You didn't ask for advice, but I cannot help but wonder whether this is bad luck or some electrical thing on your layout blowing boards. If this is unwanted advice, or superfluous, I apologize. Do you have transient voltage suppressors across all of your transformer outputs, and, if older transformers, current limiting circuit breakers or fuses that limit the amperage to your track?