Better to post good quality picture to be able to tell. But you can look at it yourself can see any physical outside damage if present at all. This doesn't need any expertise in my opinion.
You shouldnot have never taken it for warranty repair when the cover was missing. It gives them a clue. Just get a cover and then you may want to give a try at another dealership. It is quite expensive part, I have been using it since past 4 years now and so far no problem. Good luck.
535d LCI, Xenon Adaptive Headlights, ACC 2 (Stop and Go), Lane Departure Warning
Retrofits M5 heated/lumbar/memory and active backrest adjustment seats, rear heated and folding g seats, SAT Shifter, paddles (SA2TB), HUD, Rear blinds, Electric steering column, SA430 Folding and EC Mirrors, High Beam Assist, CIC, COMBOX Telematics, DVB-T TV, JBL MS-8, JL HD900/5 + HD600/4, Morel HO II, Morel Integra XO, JL 12W6v2 and Jehnert in Audio.