I've been greasing mine for 15 years and never had a problem with grime build up. I re-grease periodically and if I think about it before a trip to CA or any coastal area. I have never cleaned mine off, but if I thought they were getting damaged by grime I guess I would wipe them off and apply more grease. It does not take much just a light coating.
I guess the 100 plus temps where I live melts the grime and grease off or the occasional driving down the road in a frog choker rain cleans them, I do not know which but they are always relatively clean and go up and down easy as pie. I use a cordless drill most of the time to move them.
