Glen, they were 100% at fault due to the fact that you were parked & still, not in an area that was marked "restricted/no parking" and the fact he backed up into you. You are being way more than fair. If they don't give you a response ASAP, then you should give them your new revised offer - They need to replace your lamp with new OEM lamp. even though discontinued, they can still be had from New Old Stock. Being a dealership (no matter the brand) they should be able to source one.
Congrats for keeping your cool! I know that was the hardest part
Unless you called the cops to investigate the accident (which they won't even come out to inspect when it's done on private property/parking lot), Insurance company will just say it's your word against theirs, so they need to man up & own up............. So's you don't hafta skin that smoke wagon