LR3 Transmission Fault message

LR3 '05 V8 HSE

After a off-road trip, Engine warning sign (orange) without flashing came in. As quick fix, removed battery connector and put it back. Engine warning sign gone. Drove the vehicle, it was running smoothly.

Until vehicle get warm, I can feel transmission shifting was not 100% smooth.Otherwise, vehicle running smooth even at highspeed 120 kph

Did full body car water wash after couple of days.

After 5 days of carwash,Engine warning sign(orange) pops up again and "Tranmission fault" message also came.

Next day morning, vehicle didn't start. With the help of two boosters, managed to start the vehicle. Slowly drove the vehicle to LR mechanic. Did diagnostic, 48 fault messages found, all are clearerd. Battery change was suggested. New LR battery was installed. No warning message came. After driving 5 kms, following message came in :

Transmission Fault limited gears available

Did diagnosis, following are the results:

1.Transmission shifting 3 - 4 gear
2.Transmission fluid temp. sensor

LR mechanic suggested tranmission needs to replaced/fixed.

Also checked with another Auto transmission specialist. He also did diagnosis, suggested to fix transmission with repair kit and sensor computer needs to be replaced.

Is this electrical fault or transmission needs replacement/fixing :confused

I have read other posts in site, if I change brake light switch & bulb, will it help.:help