The manual lever position switch might be worth a try, it mounts on top of the trans below the waterpump. Run the car like 15 minutes, put through gears, put in park, check trans fluid, if really overfull, you have to drain it out till the right level is indicated. The 240 SX is rear drive(correct?), it would be easier to fix the 240's head gasket/timing belts than the trans on the Mystique, if you have to pull the trans. You might not have to though. Good luck, it's good you can walk to work, so your job isn't threatened by lack of transportation. You should have 2 good cars if you fix both