6180DW reboots on its own

[mreg45]

I have an HL-6180DW black laser. Printer works great. I have it about three years (about 70,000 prints) and tend to leave it on all the time as it goes into deep sleep. For the past few months it's taken to randomly rebooting itself from deep sleep. Sometimes this happens in the middle of the night, which is of course, annoying.

Any idea what it can be? I've changed the plug from a power strip directly to the wall, to no avail. No settings change seems to matter. Otherwise it's fine.

Thanks for any help.