The PTO for TEN-TEC transceivers was designed by TEN-TEC engineers in the early 70’s. In order for the PTO to operate as designed it must have the proper grease. The engineer designed the PTO to use open gear grease. Open gear grease was chosen because it is very tacky and stays in place when the main tuning knob is rotated. If a thinner grease is used there could be premature wear to the bearing race or inner drive shaft.