Time to get under the auto and tighten down the wires on the OD solenoid as well as top off or change the fluid in the OD.

From this side of the pond it seems like the connections are loose and dirty. The breeze under the auto at speed is probably enough to cause loss of OD function.

It may also be that the fluid may be low and foaming or just old and foaming. air does nnot work as well as fluid for pressure situations. Over a period of time it may build up and hold but not right away.

Duane