Maybe a dumb question, but are you sure it was full after the oil change, then gradually lost oil, or did you not see the oil level immediately after the change? I wouldn't jump to the rebuilt motor conclusion. It's most likely burning oil, not leaking it. Have someone trail behind you and find out when it's burning it (blueish smoke out the tailpipe, if you didn't know), such as on cold starts, off-idle, or when you really put the hammer down.

My first guess would be valve stem seals. Often times, if it's a head gasket, you'll burn coolant, as well, so keep an eye on that level.

P.S., that Corolla better be stock and stay that way.