Ok just to update this in case it helps anyone else....
we diagnosed the fault, p0763, not to the solenoid, but to the spade connector that attaches to solenoid c as open circuit. We don’t know why, but unplugging and re seating the connector fixed the problem and the car now runs with a fault free box and manual mode is available again.
p0768 solenoid D was also throwing a code intermittently and showed high resistance from the ecu loom plug so that spade connector was re seated as well. E was also seen with a fault on 1 occasion.
the input turbine speed sensor fault p0715 we presumed was caused by the box not selecting the right gear and has not shown a code since obviously with no corrective action taken.
Question remians... why would a clearly attached spade connector go open circuit while still connected? The solenoids sit in atf in the sump. They were clipped on, in place, as you would expect. Nothing was visually at fault. With a meter attached to the white with blue trace wire to solenoid c we could see the cnnnection being made just by wiggling the plug to solenoid c as it sat in situ. Removed the plug, cleaned the spade connector and the solenoid tab, refitted, all good. Resistance showing 12 to 13 ohms.
...but for how long? I know it’s common practice for autobox connections to sit in oil but oil does block an electrical signal, and the fault did go from intermittent to permenant over the period of almost a 6 months. D and E showed high resistance of up to 18 ohms, so they were cleaned as well, and if left probably would of gone the same way. They were showing 12 to 13 ohms on re assembly after cleaning.
can only assume some sort of build up on the spade connector and tab on the solenoid caused the fault. Weird.