It seems from what I have read about the Magic Tilt trailers that there are caps that fit over the ends of the wheel hubs to cover the grease fitting and spring inside the hub end. Assuming I am describing this correctly, it would appear that these covers are intended to keep dirt off the spring and grease fitting inside the hub/axle end. Do your trailers have these covers or end caps?
It sounds like youn are referig to Posi-lube hubs. I'm thinking the caps you are refering to are the ones with the rubber plugs you remove to grease the hubs. The hubs with the springs and fittings are called Bearing buddys. They are much different. Google Bearing buddys. Then google Posi-lube hubs. Study the diagrams
Cat-Man-Do,
Also check a recent thread in the CP16 forum titled Trailer Puzzler: hot hub.
Dave