Thanks for the info. I would describe the missing part as a metal cap that covers the back of the arm down where it meets the bracket on the side of the motorhome. It would be a curved piece that goes on from the back and covers the nut, wires and stuff that go up inside the arm. I'll check those sources you mentioned. Thanks again.
Maybe some part numbers to look over to see if it is what you have and need?
This is from the "parts catalog" here: https://catalog3d.winnebagoind.com/menu/Parts.htm
First pic is what it shows for the total, next is two different part number by date, before or after 11-25-2012 and then a breakdown of parts for the later group. May be some help if you get into it that far?
Now if you knew who that vender Q789678 might be???
2015 Winnebago Vista 31KE on 2014 chassis