The “Black Goo” Problem
All original IBM 5100 systems will have a foam pad that helps keep the cards in the A1 board in place, when the system is closed up. This foam inevitably begins to deteriorate over time, even if the system is kept in a temperature-controlled environment. The foam becomes brittle and starts to flake into small pieces. The portions under pressure from the cards form a kind of syrup or tar consistency, which becomes very messy to remove.
Removing the pad carefully, I was able to preserve the original sticker-back and pad on a Styrofoam base within a ziploc bag. Then use a vacuum to remove any remaining loose debris. A cardboard insert is used as a substitute to the original pad for now, as additional work is needed to remove the residue from the top of the A1 cards.