Thanks.
Well spotted. That's my old auto with his eggspensive leak. Right at the bottom of the side plate from where the drip is, along the seem for 1 inch to the right in the pic.
I was going to have a go taking my current auto apart if needed but a magic oil swop seems to have settled the problem after driving 50 miles. chance of the problem happening reduced as miles increased. I have a second batch of oil to change again just in case it happens again, but I think the problem is now solved. May use that in a few hundred miles time rather than having it sat there doing nothing. Sticking solenoid or something hydraulic/lubricated which needed a clean through perhaps causing the fault. Can't really do anymore than guess/summarise what could have happened. May never really understand what was wrong but I'm still intrigued as to how the auto works. So I recently took my spare broken one apart. Only removed the solenoid pan and side plate + the stuff behind it as built sections, then put it all back. Will travel all the way through the whole box to see what's what eventually and pull all the friction plate apart too. I struggled with the 2 larger bolts on the top right of the side plate which triggered this thread. 17mm if I remember correctly. As the auto box will never be used I bodged it but intend to be able to cope with shallow nuts without damaging them in the future.
My hawkeye is currently watching the brake signals to the auto to confirm if the auto does receive the brake pedal signal when braking, if the fault happens again.