Just a couple things to check...
Have you verified that the driver board transistor for that coil is not dead?
I'm assuming you have 43v at the coil as it is daisy chained from that coil on, so another coil would not be working, but worth asking.
When you said you cleaned the molex connectors, did you just clean the headers? They might work but if the pins on the connector are bad, it would still possibly not work. Wires can break off or the pins can be broken in the connector and make no contact.
Check the Diode on the coil as well, doubt it would cause it to completely not work, but if that failed it could have caused something else (like the transistor) to fail.
You can check http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Solenoid_Driver_Board_Issues on pinwiki as well for some ideas.

Yes, it does appear to be Q10 which is a TIP102.
Check the link I posted above to Pinwiki and it tells you exactly how to test the transistor in circuit, so no desoldering. Just need a DMM and to turn the power off.

Glad you got it figured out!
Those cold solder joints can be an issue like that.
Might be worth checking the other boards just to make sure you don't have any more.