I tend to believe the so called myth for one reason. We had the heads rebuilt on our old fullsize Dodge Van. The exhaust valve seats were beat up like mine were on the 6. That was at 85,000 miles. We had hardened seats put in it and drove it for another 200,000 miles, only had to replaced valve seals @ 190,000 and when it finally spun a bearing @ close to 300,000 miles, we pulled it apart the valve seats looked great... without them we would have had to do 2 more valve jobs.
