[Top_Ghia]

I fill them with 6.5 L of fluid when servicing them. That is what comes out when you drain them at 60.
1.5 extra litres certainly wouldn’t help anything. Maybe someone serviced it but only drained 1 section.
I have no idea why your flush worked. Maybe it has freed up a sticky solenoid.
These transmissions are sensitive to oil quality and certainly do play up if neglected.
Well done and let’s hope it keeps behaving itself.