In case you didn't know, you can get wiring and plumbing (and other) diagrams from Winnebago for your motorhome. I actually had a 1990 Chieftain up until about 6 months ago. I had it for about 13 years. So, I had lots of experience fixing and/or improving things.
Here's the link for the manuals....
http://www.winnebagoind.com/resources/manuals/Second, I had an issue with one of the corner pieces on my 1990 as well. I was able to order the part from Winnebago.
You can figure out the part number from their website....
http://catalog.winnebagoind.com/menu/Parts.htmIf you drill in to your model, the part numbers are definitely available for the end caps. You should be able to google the part number and find it for sale at Winnebago.
For example, I looked at what I think MAY be one of your end caps for the bumper and came up with the following link....
http://www.winnebagooutdoor.com/Winnebago-Industries-078578-02-000-Bumper-End/dp/B00PHCTQYWGood luck with your motorhome!