The rear decklid bumpers are liquid-filled. Over time, they leak and require replacement. Some XLRs had a piece of adhesive-backed weatherstripping installed by dealers to repair a known leak issue on the early models. It also degraded over time and left a tarry film.
If he is ta!king about the trunk bump stops i believe they are solid rubber molded to a stud that just turns to goo. I have new oem if someone wants to cut one apart.The reproductions are very soft and did not last but a couple of weeks On my customers car. Workmanship was excellent. Hope he makes them out of harder rubber next time and molds them to the stud so they dont pop off.