I'm not talking about the local ethernet MAC, I'm talking about the MAC Address that the modem presents to the cable line. On the cable interface. Look, here is what I'm talking about specifically. Attached are two photos. One of these is the label printed on the modem itself, and the other is a screen shot of the modem's status page.

If the WAN MAC address is screwed up, the modem won't work on the network. And it's been screwed up. I believe that Comcast has the ability to brick a modem by remotely altering these kinds of values.

This particular modem I think it took them several tries. The modem has been rebooting itself every once in a while and losing all its configurations settings each time. I think in the few months I've owned it, it's rebooted itself maybe four times, intemittently. I think those reboots were all attempts to fuck with its configuration.