Stiff Tap?

I have a mixer tap on my bath with a little pull up lever to make the water go up to the shower head, gradually this lever has become very stiff and now is a real nightmare to pull up, i was wondering if it may be a build up of limescale or something, but would love to be able to sort it without having to replace the whole tap as the rest of it works fine, any suggestions gratefully received :O)