I have a TiVo HD with lifetime service and have just ordered a Roamio Plus. I want to continue using the TiVo HD in a secondary room, but it has symptoms of a failed hard drive (stuttering, freezing, and "Fail 7" result on kickstart 54 tests). I have a My DVR Expander but it checks out fine in the drive tests.

Question: I want to spend a minimum amount of money to repair the TiVo HD's hard drive. A local seller has a used one for $40 which they say works without any problems. If I buy the used TiVo HD, could I just put its hard drive in my TiVo HD without reformatting hassles? I assume it would require unpairing the Expander and that I'd lose all the existing recorded content. I also realize this has some risk because I don't know how long the used drive would last, but $130 for a new drive is more than I want to pay at this point.