I've put the pieces together and came to this conclusion about my 508.
Handle grip: Sliding around in the car trunk and hitting something probably sharp, gouging out pieces of the handle grip.
Broken rear wheels: Sliding around in the car trunk and hitting something. (The right rear wheel finally fell off).
Rust stains on the bag: Being stored in the trunk which most likely had a leak, or somehow allowing moisture to get in. No carpeting or rubber mats on the floor. The floor rusted, that's why there's a very distinct pattern on the bag (lines).
The 508 was riding in a rather old and junky Mercedes for a month. Shame it got treated like that, and I think the seller should have told me what happened, instead he kind of cheated me. Absolute shame...