After perhaps a month with the replacement Roomba, I noticed an odd screeching noise, no dog hair in the vacuum’s bin, and increasingly hairy carpets - despite regular runs with the robot. Not good - looks like the brushes stopped turning.
Called iRobot Customer Support and got connected immediately (a surprise). This time they want me to ship back my failed unit before they send a replacement (not unreasonable if a bit of a drag).
Funny thing is the carass of the first failed Roomba is still here. Bet I could take both apart and put together a working unit - but that would no doubt void the warrantee, so I am not going to try.
This thing is useful - when it works.