Back in the day when your boat was built the bearings in traveller cars were not captive meaning there were held in place by putting the car and bearings in place at the same time, if the car is removed from the track the bearings will fall out. On your traveller, the car may have been installed on the track before installing the track, thus to access the bearings it would be necessary to remove the track end fittings and perhaps the track itself. The car can then be slid off the track with the ball bearings coming loose and scattering. Hold a cup with padding in it to capture the bearings as they come free.