2004 Kia Sportage whining noise when clutch is released

As mentioned above when clutch is released the gearbox makes a whining noise and disappears when clutch is depressed. The whining noise is also audible in all gears except in 4th gear. I have been to gearbox specialists who advised that my cluster gears must be replaced with the release bearing. Kia mechanic tells me it is only the release bearing. As the parts to replace will cost approx. R11,000 (rands) it is essential that I must know exactly what the problem is before spending so much money. One more question. If it is the cluster gears, can I drive it with the noise? Will the gears eventually break. I intend to pull a small caravan (750 k/g) on a trip to Namibia. Will the gears last. The whining noise does not bother me at all.