Running oil in front wheels and trailer axles did not become popular until later. Here is a link the company that developed the hub oil seals. http://www.stemco.com/Company/History/tabid/66/Default.aspx Most trucks that were still in use in the 60's were retrofitted. All it took was a Stemco seal and a wear ring on the spindle. I haven't run oil in hubs in about 15 years. While the hub oilers were a big improvement over packing wheels with wheel bearing grease, running a semi fluid grease such as Mobillith 007 in steering and trailer is more cost effective now. I have practically no seal failures any more.