I don't think it is good practice at all to use their in house watchmaker for a grande complication piece. Even if the watch comes back "working" you will have no idea on what damage will have been done where you can't see. These are super finely finished parts and, although it takes forever, it is a much safer bet that the Patek watchmakers won't leave marks on parts and will stand behind their work. Also, they have access to all the possible parts they need and will be far more likely to "fix" a bad or marginal part rather than using a brand new one.They simply won't waste their time with a bad job...