2.) Modems and STB's that go through an endless refurbish process. Techs find bad equipment which is sent back and then repackaged and given to another customer
And this doesn't happen with cable? The answer is yes, yes it does.
I can't really answer you question about the cancellation window, but there are direct users that will probably ask you to post in the direct forum and help you.
To me it sounds like you have two issues, the DVR's drive is dying and a connection issue. With the DVR drive dying so much. Are you sure you don't have it near any magnetic sources? If you still have a CRT TV having the DVR right on top isn't a great place for it.
More people will probably be in soon to ask your more information like to run uverserealtime and post your graph.