What Ford is talking about is a rubber sleeve that is on the output shaft ( normally but not always) . These are most common on automatic applications. The inside of the yoke slides over the sleeve keeping oil out ( to a point) . it's always a good idea to have some grease on the splines , but not too much.
'66 GT350H-3 time cover car - Car Craft July'77,Modified Mustangs and Fords Feb2011 ( w/article), Mustang Monthly June 2014. Bracket raced by me for the last 44 years. Yes it is a real one.
'68.5 R code GT fastback
'67 Ranchero 408W -427 glass hood
'78 F350 "Oleynik" car hauler
Ford Experimental parts collector