the spout is sealed to the tap body by a couple of o rings u will need to take the spout out it will either be held in by a small screw at the back (might be under a cover) or turn the spout so it is at right angles to the sink ie over the top of the heads & wiggle it to get it out then replace the o rings
Keith Gillyon Plumbing, Heating & Building Services. Southampton., June 2009