Bob, could you explain to us novices, what actually causes seats to come loose? When you talk of a seat not being centered to the valve guide, does that mean it loads the seat to one side and tries to pop it out like a bottle cap? If there is a problem with the casting or the alloy, (and what is the liklihood of this?)would welding the seat area and remachining it be worthwhile or a crapshoot? It would seem like there would be a way to determine the underlying cause of this, I remember back in the early days of production aluminum heads they had problems that obviously got worked out. If the seat is strictly a press fit, would the likely culprit be poor machining tolerances? Also, who manufactured these heads anyway? I appreciate your help! Lee.