The down arrow from a VT100 keyboard might be close enough to work on this keypad. Also, I'm sure that the down arrow isn't the only key to have a plunger cracked at the corner if some keys feel "sticky". Whoever ends up with this terminal should check how many keys have cracked plungers. I might be able to help them.
To the OP, yes, you should sell it. If you have no use for it yourself, sell it to somone who would want it. You will have no trouble finding them.
Lou