Didn't know that, glad I didn't toss my original!!As a VC-120 user for the last 11 years, I still regret that i didn't just rebuild the original canister but threw it away.
Seems you can just file down the edge at the top where it's rounded over and the top comes off. Dump the old charcoal, clean the valves, throw a new filter pad in the bottom, refill with new charcoal from the fish store, and epoxy or silicone the top back on.