I took my Winnebago Sightseer to my dealership, Awesome RV in WA, yesterday for an oil change and generator service.
While there I asked the parts guy to order the screw cap cover for the corner trim on my slide out. It looks just like your second and third pictures. I believe they are even the same color.
It was too late for him to call Winnebago yesterday so he said that he would call today.
If I remember I will ask for the part number and send it to you.
To order you will need either a part number or your vehicle VIN and Serial number.
You can order directly from Winnebago. (1 800 537 1885) [email protected]
An email will take several days to receive an answer.
Another choice is Lichtsinn RV (1 800 343 6255) located about a mile from the Winnebago plant in Forest City, IA.
Or you can order from Mobility RV located about 25 miles from the Winnebago factory in Iowa. You can contact Mobility at WinnebagoParts.com.