When we were at MORryde a couple of years ago having the 2" risers put in the techs working on our trailer were adamant I change over from oil bath back to grease. They're thought process is these RVs don't travel enough and are parked too long causing sections of the bearings to "dry out". I know, I know, we've been over this a number of times. You for one would lift and "spin" your wheels periodically BUT the techs at MORryde "insisted" that most won't/don't and there in lays the problem...... bearing failure.
Just saying, that's my story and I'm sticking to it.
Dan