A trick I learned while pan car racing that works great for off-road cleaning and lubing bearings is to use trumpet valve oil. You can get it at any music store for around $5. I also use the Integy bearing bath thing that vibrates with the oil and it will clean anything out of the bearing and lube it at the same time so after 5 minutes in the bath they are ready to go back in the car. It even works on shielded bearings without having to remove the shields!