Oh man, that is a great router, definitely go back to that then, no reason to drop $$$ on a new one (though if it dies, get an Asus or Apple, they're both superb).
As for the TWC modem lease, I can tell you thankfully that it's really quite painless. Basically you call in, tell them what you want to do, they'll have you read the MAC address of the modem (listed on the box and the modem itself), they have you plug it in, and boom, after they get the number linked to your account, you're good to go!
It was one of the first things I did when I got TWC at my new place, it's the best option where I'm at now (I came from FIOS, which was awesome but pricey, but that's a whole nother story).
You can also use the TWC online chat support to request the switchover as well. But yeah, it's super straightforward. Basically all they need to know is that you want to use your own modem (so they can drop the lease fee), and what the MAC number is. Good to go!