Hi Iain, the bearings in the actuator arm are sometimes held in with a retaining compound, so you will have to warm it up a bit with a hot air gun and then quickly knock it out with a piece of tube that fits the outside bearing ring. Don't get it too hot or you will damage the bearing. Others are just held in with a tiny screw in the side of the arm body. The photo below shows one with a screw holding the bearing in the arm.