For the rear left bumper area it's very likely to be the BRACKET-REAR BUMPER SIDE,LH, Nissan part # 85013H, about $30 give or take. If the bumper is bumped hard enough in the right spot (perhaps by the previous owner) the plastic bracket that pulls the bumper close to the body will stay in place, but partially crack and slightly drift away from the body and end up looking like your bumper. See the attached pics for an example where the plastic around one of the connecting bolts broke off. You can access this part without fully removing the bumper, just remove all the bolts and snaps on the LH side of the car and the snap just below the rear fog and you can get enough clearance. If you want to be really careful you can remove the entire bumper, it just takes longer.
For a second view, take a look at NickTurnon's car below (see his build link here
NickTurnon's 370z Build). On his silver Z the bracket is white in color. You can see where the bracket is located here:
