The grease very rarely gets where it's suppose to go.
It is suppose to go into that little hole in the OD of the bearing.
Even if you line up the zert fitting with the hole I don't think the grease will go into
the hole.
About all you can do is pump lots of grease in it to fill the void between the bearing
and the flanges, that will help slow down the water from coming in when your floating.
The mud and gunk will surely fill that little oil hole in no time.
Keep plenty of bearings in your tool bag.