Thanks for the reply.

I dropped the oil and nearly 5 litres came out (brown and burnt smelling) and it took around 5 litres of the dexron 3 oil I bought today.

I gather that only around half of the overall amount of transmission oil will drain out as the rest is in the torque converter, so I plan to change the oil again and change the filter also this time (filter ordered today from main dealer for £75!).

Has anyone done this? How many miles did you do before changing the oil for the second time?