Thanks. I don't believe the bumper has ever been in any sort of incident, or if so, I've never seen any evidence of it. As far as decorative, I can see steel structural material where the bolts goes through and the plastic covering is just decorative. I'll take pics if I have to take the cover off to hold the bolts.
Behind the plastic cover, the carriage? bolts go through the bushing you referenced, then through whatever material is on the other side and then flat & lock washer and nut. I believe it's simply the material that's deteriorating and the springyness of the bumper that's pulling it through. I'm certain the angle aluminum will keep them from pulling through and if I ever snag the bumper, I'll deal with it then.
What I was really hoping to find out from someone is what the material is, how is it mounted and any possible solutions for repairing or replacing it. It is certainly located in a pita area to work within.
I haven't called Winnie but I've had mixed success with them - maybe Winnie parts?
Guess we'll see how the thread goes. Thanks for the input.