i have a 02 octavia with 26000 miles on the clock the problem is the speedo is very erratic i can drive a full day and not clock any miles up and some days the speedo is all over the place even when i am stationary and in neutral the main dealers say it is caused by a problem in the gearbox other mechanics suggest an electrical fault can anyone else help

an electrical fault from the sender unit in the gear box prehaps?

Either the sender or a loose contact/dry joint in the speedo head end.