[Laird Scooby]

It sounds like your old 960 had an igniton related problem and was feeding this information to the gearbox ECU which then responded by chaningn up and down.

However, without knowing exactly which box you have in your 940, it's probably not possible to say, rough rule of thumb is if it doesn't have cruise control or Sport/Economy modes on the gearbox, chances are the box won't be effected by the rev counter doing its little dance.

You're probably right on the humidity causing the problem but it might be worth removing the instrument cluster and cleaning the connections on the plugs that plug into it and the tracks of the PCB where they plug in.

Also worth removing the ignition amplifier module, cleaning the mating surfaces of the back of it and the heatsink on the inner wing with a non-abrasive solvent cleaner and adding some fresh heatsink compound before refitting it and checking the earth connection for it.