If it cracked sitting in storage, it was put on too tight.
If cracked during operation, then you need to lube the worm gear and rocker gear up on top. It takes two people to do a good job unless you take it apart. Have helper raise the antenna. Stop after one or two turns to apply a good quality water resistant lubricant. DO NOT USE WD-40!
If you have the wrench to take the antenna shaft out do it that way. Take nut loose and pull worm gear shaft out and lubricate it good.
Go to page 5 for directions on lubricating.
Winegard manual