Our 2004 Designer 5er had the same riveted plastic plate when we bought it secondhand, and some of the rivets were missing. I replaced it with a 10" white plastic plate that you do indeed just push on. The old one was square, like the pin box, but the new one was round. It seems to work just fine - no problems so far. Sure beats the grease you would otherwise have to put on, which looks just like a semi-tractor grease plate - ugly. These are available at most any camper supply, not all that expensive (I think around $12 or so), and you will be happy with one. Enjoy your new Eagle !
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.