When using the bearing protectors over filling the hub with grease will cause grease to be pushed past the seal at the back of the hub.
Wheel bearing grease leak.
Your wheel bearings were probably originally lubed with a lithium 12 complex grease a perfectly good grease for wheel bearing use even on a boat trailer if it s maintained.
High performance vehicles that drive through water regularly will need water resistant grease to protect the wheel bearings from oxidization.
Inside the wheel bearing is a tremendous amount of grease that keeps the bearings running smooth cool and free.
Grease is leaking from the bearings.
The wheel seal is supposed to fit very tight in the wheel assembly and protects the wheel bearings from dirt water and other debris that can cause damage.
Just a quick video on what i do to maintain and keep grease in the bearings on a trailer.
The bearings that support the wheel ends are heavy duty and able to handle most any load you can put in or tow with your ford super duty.
So always pick a wheel bearing grease that is designed for the temperatures of your application to avoid grease leaking out of the bearings.