So, Other World Computing were champs about this. The 8tb drive I bought was on sale, used, but they just upped and replaced it with a new one. They have given me unflinching support for 20 years.
Also, learned a thing about Backblaze. It installs an invisible folder on your drive that gives it a unique ID and if you clone that drive with CCC it clones that folder, and confuses Backblaze. You have to delete the folder contents, then re-set the new drive in BB prefs to get it to back up under the same name. Fortunately it’s well-documented in their FAQ’s.