Like others my knee-jerk reaction is ‘line voltage’. It is odd that it functioned so well for you for so long, is moved to a new location with a new source voltage and things go south. When I sell things I sell them “as is, where is” for just this reason. However, like you I would feel some responsibility in following up to see what the cause was. If you have the wherewithal I would have the motor tested. Depending on how trustworthy the person who bought it is, you may just tell them to go and have it tested.
"A hen is only an egg's way of making another egg".
– Samuel Butler