Eh, the seals main job is to keep dust out. You should be rotating the upperstructure while greasing. What happened to the seal? Did it just fall out?
Like Shimmy said.
What happened to the seal?
Did a stick come up and hit it.
There is a reason I ask.
People tend to over grease the slewing bearing and this can cause the "dust" seal fall out.
If the slewing bearing has excessive wear you will not be able to keep the seal in. In which case the expensive part comes into play.
If it just got torn out with a stick or rock it is not a big issue to replace, I have done many.
We were able to buy the seal and install it. Just comes on a roll.
The groove had to be spotless clean and grease free.
A few dabs of Loctite 380 (Black Max) in the groove every so often and just push it into place.
Use the black max to join the ends together and Robert is your Father's Brother