Mike,

4 bolts/nuts (don't know anymore since it depends on having a trailer hook and it has been a long time since I last removed one) with a 13mm head under the taillights. The sides of the bumper are aligned with 1 bolt each (10mm head) and these bolts are located behind a latch in the plastic trunk panels. No bolts or nuts in the middle of the bumper.
Once you have removed the rear bumper you have to get out 3 Phillips screws at each side of the impact strip after which the strip can be clamped out of the painted bumper shelf.

good luck & greetingz,

__________________
1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)