Disco series 2 auto box gremlin HELP !!!!!!!!!!

[powelljem]

Hi learned people,

Have just aquired a 03 discovery 2 automatic which has a wierd fault.

Start up engine, select any gear nothing happens, wait with engine running perhaps 10-15 mins or less sometimes, gear engages and off we go.

Gears change up and down ok and box is smooth and not noisey in any way,this problem does not occur everytime you start the vehicle.

Tried all of the usuall things,select all optional gears inc sport and low/high range,
to no avail,turn engine off and on (works sometimes)has had new xyz switch fitted.

Garage is telling me it needs a new box, but i think it aint broke and its a electrical problem, vehicle has only done 63 thousand miles !

Regards Powelljem