I have a new Z20 Purchased 12-15-2018 tandem axle trailer with vortex maintenance free hubs (6 years or 100000 miles). I noticed one of the caps missing on the one of the axles. The grease made a mess on the wheel. The caps are a screw on cap with a rubber o ring. Bass pro replaced it at no cost. I am bringing this up because after I screwed the new cap on I decided to check the other three caps and another one was loose. Recommend you add this to your checklist. If you have to buy the cap it ranges from 20-30 $$ plus shipping. Just an FYI.