Reese sells a grease they say is specifically for use on the ball and you used to be able to get it at Walmart in a small blue and white tub, BUT I have used any type of heavier wheel bearing grease in the past. You must use some type of grease on the ball because there is so much metal on metal force on them.
The friction between the ball and coupler, as you have found out, can wear out either the ball or the coupler or both. In addition, many members have found that the friction will loosen the ball in its mounting from turning.
Do not use wax paper, silicone spray, or WD40 as that does not provide enough lubrication nor does it last. Best idea is to wipe the ball and coupler off after use and then re-apply a heavy grease before the next towing session. That way, you keep the area somewhat clean and don't get grease all over you or others, and you don't have a sandpaper effect of the dirt on you ball or coupler.
Barney
2004 Sunnybrook Titan 30FKS TT
Hensley "Arrow" 1400# hitch (Sold)
Not towing now.
Former tow vehicles were 2016 Ram 2500 CTD, 2002 Ford F250, 7.3 PSD, 1997 Ram 2500 5.9 gas engine