Trackers have the grease zirk fitting on the axle hub. I looked it over, and it squirts grease in the bearing, somewhat. I still strip them down and repack every season or next.
19 years on bearings is probably a long time. Depends on how far you pull your boat. A good indicator is tires. Most Bias tires only last a season for me, radials up to 3 or 4 years. Bearing inspection and replacement is about the same schedule. You can usually see the slop in the bearings with tire wear, unless the bearing lets go prematurely.