They also use wax to level across the seams between the slate pieces, I’ve seen them moved as discussed and fracture/disturb the wax causing width wise ridges under the felt from the table flexing. If it’s due to be recovered, I’d take it apart myself, set it aside and have it reassembled & recovered in a quality felt if it’s worth it to you. I played for years and had a 4.5x9’ that I loved several times.
