The liner may just be choked in with sand or time. Be gentle extracting it and don't use the suspension harness to pull, I imagine you already ruled that out. Just work with the edge of the liner, it may have been crammed in tight and grit holds it. The liner looks early, is there a grommet in the front center? The covers originally were HBT I think, like the head harness...which that harness appears to be. Once you get it apart, we'll see more.

Yes, you did fine for cost.