A square one piece sealing member for a slip type driveline assembly to prevent loss and contamination of lubricant. The sealing member is made of a resilient material and has four walls and integral radially inwardly extending ridge members. The walls and ridges generally complement and mate with the square end of a slip yoke that has four grooves on its surface to receive the ridges. The walls are joined to four radially inwardly extending walls which in turn are joined to radially inwardly converging square pyramidal walls. The pyramidal walls terminate at four radially outwardly extending reinforcing ribs.