White lithium grease.
Silicone to make a gasket, try and use marine grade if you can.

 

I used the rover (D1) to pull a tree out of the front yard once.
Figured it would work out as the Rover has a strong frame.

I don't dare take it into mud.

I am glad you are using it for the intended function.
But, dismayed at the labor in restoring the rover to fit and form.