We running a Airborne also in our gameroom. We had exactly the same problems with the microswitches from the droptargets and the sudden ball end. We also replaced all the microswitches at the droptargetbanks. One of the transmitters in the trough was bad; replacing it cured the sudden ball end problem. We put the game in testmode, reading the switches without balls in the trough. Then from time to time one of the opto's in the trough was registering. It could take 30 minutes or more before this was happening. This revealed our bad opto.
With this kind of problems it is also worth to inspect the 0.100 connectors at the optoboards and the switch input board.
Marco