It requires a fair bit of twisting force. It tends to start separating around the light button first, and you can begin by working something in there. Note that you may end up breaking some of the clips that hold it closed, which may or may not have any actual effect.

One thing to check is that it may not being the serial port that's bad, but the cable. I've gone through several that have failed at the connector end (intermittent connection, like sometimes if you bent the cable in one direction or another, you could get it to work).

Also, if you're thinking of "re-painting" the key contacts, that tends to be a VERY short-lived fix. But if you see an oily-like substance on the circuit board, cleaning that off may restore operation for a while.