It depends on what chipset you've got and what problem you had with your 360 initially. Depending on the issues (and if you've got a special box like a Halo 3/Resident Evil unit) they'll likely fix your actual unit. Generic Older Xenon units got a new heat sync and get sent back out. Ones with dead drives are given 'new' refurbs and are sent back out as well. I'm not sure what needs to be done with the 374 errors.