Help needed for 6n automatic transmission problems

[miapolo99]

Acquired recently a 99 Polo auto, advertised as in ""excellent condition" drove 5km and the auto dropped into angel gear at 50km/h, had to pull into 3 to complete journey. Took car to qualified VW mechanic who suggested changing oil and filter. On examination only the inner filter was found. Ever dentally filters for this model are scarce as rocking horse .....but one was found and replaced. After much money was spent gaining a safety certificate the problem is still there.
Has anyone else encountered this problem and more important is there a cure out there? Someone suggested the throttle sensor may need replacing? Also has any body found an outlet for auto filters?
Thanks in anticipation.