Have you checked the wire from shifter to the solenoid? I don't know if it's the same setup as the 240 but I fixed my friend's o.d. problem last week it was the the aforementioned wire. Her overdrive would work sometimes and not others, finally the relay and fuse were fried. What was happening was that the wire was losing it's insulation so occasionally it would short out causing an intermittent deal. Finally it wore off to the point that it was shorting out and frying things. Worth a check for sure.

Good luck!

Kirk S.