I can drive around town and on short journeys and never have a problem. However, if I take a journey that lasts around an hour and a half, there is a definite 'clunk' that feels like it comes from under the pedals, the auto box warning light comes on on the dash, and it stays in a high gear. There is no warning on the multi function display, and it drives fine if I change gear manually. On a motorway, I can carry on driving for hours. If I stop the car and turn off the ignition and turn it on again, the warning light goes out and the auto box changes up and down normally for about ten minutes before the fault reoccurs. If I stop the car and leave it for about an hour, then all is normal again.
The transmission fluid was changed about 200 miles ago, but is now looking burnt and brown.
I do not know if this is a common fault on these cars.