I got a heavily used Wheelock AES-DL1-WM with an unconnected capacitor. Should I attempt to resolder it? If so, what would be the best precaution if I do?
If the solder joint cracked off just use a desoldering pump or braid to suck away the excess solder, and then resolver it to the board.
If the copper pad separated from the board, you would be best just getting a different device. You could try to solder a jumper wire from the capacitor lead over to a equivalent location along the trace. Just make sure it would change the basic circuit design, obviously it will look different.
If the capacitor itself is damaged again a different device is your best bet, but you could replace it with a new component with the same microfarad value.