I agree with zigzagrv, I wouldn't grease it unless that is what the manufacturer suggests. Years ago I ran into an issue with PullRite, they recommended using a product called Slip Plate, a dry-film graphite lubricant.
Master Tow ManualWhen in doubt I'd contact them.
Phone: (910) 630-2000
Toll Free: 1-800-522-2190
E-mail: mastertow@mastertow.com
Two Wire Fox Terriers; Sarge & Sully
2007 Winnebago Sightseer 35J
2020 Jeep Gladiator Rubicon