Ironbound

You're closer to my view in your seconds observation. As long as the purpose and ownership sentiment is the same, no matter what is fine to the object it will still be considered the 'same' thing.

However, if the owner feels that the change, however small, alters his sentimental attachment to the object then in essence it is no longer the 'same'.

I agree but, theseus isn't exactly around to give his opinion on the matter... so unless he shows up and says it's not the same ship i'm going with "it is, in essence, the same"

if it were something different, like a kid's teddy bear that had bits replaced until none of it were original, i'd leave it up to the hypothetical owner.

Precicesly. It's subjective, and therefore, neither answer is correct at the supposition of the other being incorrect.