Mixer Tap Dripping

[pjh1000]

I have a AREL KITCHEN SINK MIXER TAP with a water softener attached. It has been dripping for sometime. Had the plumber out and he said it needs replacing and the internal unit housing the washer/movement lever is a sealed unit and cannot be replaced. He was going to buy a new tap but I haven't seen him since tho.

So is this true or can I replace the internal unit or do I have to replace the whole tap. If so can I not buy one off ebay and just replace the internal parts or are they all different.

thanks for any help.