After a nasty “off” into the dirt I used WD-40 to clean the grit out of my three sealed 50mm axle bearings. I did not remove the shields. Yes, this is a messy process. Then I spun and sprayed them with aerosol red lithium grease. That was last season and they still feel and sound like new. I “rinse” them each track day with a 1 second shot of Tri-Flow. This keeps my axle clean and bright too.