The dealer is going to be pissed once you drop it off. Just forget about it. If you want an early 90's 5 series go and buy one, its not that rare or expensive of a car to get involved like this in.

Don't tell the dealer, just do it. Get it on their property and leave, I'd do it after work hours.

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2006 CL500
2009 C300 4matic
1969 280SE
2023 Ram 1500
2007 Tiara 3200