bore groove 48 if desired outer wall 54 may be constructed parallel to mating inner groove wall 50 so that when locked in place they will be flush while the present invention is disclosed in combination with slip spline assemblies that is designed for periodic replenishing of lubricant it may also be used in assemblies that are lubricated for life in such assemblies bleed opening 41 see fig2 and 3 would be eliminated and a boot type seal would be employed in place of seal 28 and retainer 30 in typical applications of this type one of the spline teeth is removed to prevent pressure build up and facilitate back and forth flow of lubricant during stroking also the flexibility of locking portions 46 may be reduced by reducing the number of notches 44 which extend from the end of plug side wall 40 or increased by increasing the number of notches sealing plug 36 may be a stamped metal part which is finished machined or alternatively a one piece molded part made from a suitable plastic material such as nylon or a nylon glass filled combination from the foregoing description it is apparent that the advantages of the present invention result from the combined relationship of the flexible locking portions of the sealing plug and its cooperation with the annular locking groove in the yoke bore the arrangement provides a positive and economical way of retaining a sealing plug in.