Which as you wrote them are the same part numbers. Now, I had answered this before, but can do that again it here.
Tecnically speaking there is no designation such 7S26 and no letter. Since its introduction, Seiko has placed a letter at the end, that is A, B, or C in chronological order of introduction. When someone refers to 7S26 and no letter, in a technical context that can introduce ambiguity.
To help on the matter I have summarized all these changes is a document, here's it again:
Just go on Ebay or the Internet and search for the P/N detailed in the document above. You may need to add or omit both the leading zero and the separating dot in order to get all matches.
Note, you can be asked ridiculous prices for either new or used individual parts. The best approach is to get a complete mov't or watch for cheap, and use it as a source of parts.
No it is not, and the notes in my document explain why.
I agree with Rodabod. $360 should buy better accuracy than that. If they have any pride in their work, and want to keep receiving your business, they won't balk at taking it back in, nor at regulating it properly without charging you twice. The idea is to be so pleased with their service that you don't mind parting with the $360.