Rich, the only problem I have ever heard of is in engines that need lead in the fuel. The additives in detergent gasolines tend to erode the effectiveness of lead additives, like one hand cutting off the other. Old VW parts that liked lead might not like SeaFoam and such, but a quality aftermarket engine shouldn't care. If it's running on pump gas ... Anyway, I'll look that up today for something to do.
As for keeping the lubricant oil where it's supposed to be, I've never heard of quality products doing any real damage.