Please clarify what it is they're proposing. Are you saying you're getting a recertified "used" TV in exchange for yours? Were you having other issues besides the 3D crosstalk? Were you having terrible banding, darkened stripes, dead pixels, anthing else? I think I'd confirm it's a "brand new" TV since these issues were factory defects right out of the box. And if it's truly the motherboard causing the 3D crosstalk, do you think it's logical that all who post here and on other forums about 3D crosstalk (and there are many) have bad motherboards? All of them? I guess it's possible. Again, unless you're getting a new set, I'd be leary of that deal.
Support technicians do the best they can do but diagnosing a problem that serious over the phone is a hit and miss. And unless your replacement is new, it'd be like exchanging your brand new BMW with a recertified used BMW. If you've been told it's a new set, then just disregard this post but if it's used, does anyone else see an issue with this? Should he go along with it? If you do exchange it and all you had was 3D crosstalk, I'd be curious if it fixes that problem while not introducing any others.
For what it's worth, if it DOES fix the crosstalk issue and everything also looks great, I might go along with a replacement too. But again, I think I'd make sure it's a "new" TV that the technicians removed from a "new" carton and personally checked for issues, which is what their QA department is supposed to do in the first place. And I only feel that way because my current 75 inch set has a beautiful picture in every other way, except for the unwatchable 3D crosstalk. I'd be too afraid of being less happy with whatever they replaced it with.
Please keep us posted.