Firstly, where is it leaking from? If its from the gasket seals around the water pump body, you can use rtv sealant to re-seal the water pump.
However, if it leaks from the pulley bearing, I'm afraid you will have to change the entire pump.
Found some pink powder like substance between the top tank and radiator. the mechanic suspect need to open up and reseal the thing. But they are worried that the top tank may be broken or they break it while...