Had a DSL modem years ago that had this issue (periodically it would simply quit interacting with the DSLAM, resulting in no internet until it got power cycled).

My solution was exactly this (although without googling for a solution). A 24 hour light timer, set to power cycle the modem sometime in the middle of the night. Since it usually took several days before the modem got hung, a nightly power cycle meant that things were working properly at other times.