stiff taps

I have a 4 year old bathroom sink tap with single spout and muti swiveling control lever. Its getting very stiff to operate but never drips. Is there a way of lubricating these, I know there is no washer as such, just a plate that moves over the inlets or something like that. Could you dismantle a spray silicon that you use to lubricate rubber flaps etc>> TIA
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