I'm not a collector of fine artisan pipes, though I own a few, nor do I do restoration, so I am speaking more generally from shopping a lot online. If you are looking at a pipe as a collector or historical piece, I'd say the replacement stem is a deal killer, with the exception of the one made by the pipe carver him or herself that would pass essentially undetected or be forgiven if stated up front. Most of us on Forums are more focused on smoking pipes, so for us, a respectable replacement that matches the pipe well is mostly acceptable, I'd say. I think this is less true of Dunhills; since you are paying a lot for prestige, you want the whole Dunhill or none, though a replacement stem might be okay for someone who must have a Dunhill but really can't budget most estates. Then a replacement stem would make rather than break the deal. The main thing is, in shopping, I want the seller to know if a pipe has a replacement stem and to give an appropriate discount on that basis.