Since we are on our way to getting new bumper caps it is time to ask the membership about a suitable adhesive, On mine (the test model)all I can say it is gray and they used about 6 oz out of some sort of caulking gun and just glopped it on and pressed the cap in place. After 17 years it was still elastic and it required a scraper to remove it. What we need now is recommendations for what to buy to attach the new ones. Any chemists out there?

I'm no chemist but I have used Sikaflex when I did some body repairs on my GMC bus I used to have. I friend recommended it to me and said it was used on the panels on his Neoplan. It's expensive but really bites.

When I want some permanent stickum for dissimilar materials, I use 3M 5200.

I've used both 3M5200 & Sikaflex, & found them equally effective. They are chemically very similar.