Monobloc Tap Sticking?

Frustrated that the 6 year old kitchen Single Flow Monoblocap Sink Mixer Tap has to be replaced due to the lever sticking to almost nil turning ability.
Purchase from MFI who have ceased trading, hence brand name cannot be established to buy a new cartridge, if this is the problem ??
Lever top has been removed for inspection, but not the cartridge cover as this is very tight.
Live in a soft water area where appliances don`t become damanged from lime scale.