I grease the roller bearings liberally with marine axle grease and remove one roller from each axle prior to installation. This keeps them from squeaking, provides enough space for the bearings to actually rotate, and reduces the chance for flat spots (try it both ways prior to final installation for a demonstration). I've inspected the bearings after about 1000 miles of use and had virtually no bearing wear (mild wear on the inner sprocket surface). I've had no issues with contaminants but do not expose the Drives to sand. IMO, if sand enters the sprocket shaft area, it does not flush easily, with or without grease. Regardless of sand exposure to your sprocket shaft, the other two shafts should not be subject to sand unless you are throwing your Drive in the sand. Your light lube should also keep the bearings squeak-free if you are not greasing.
