Well its a 20 year old Mercedes its going to have many issues and need several grand in defered mainaince. Thats pretty much a given and not surprising.

But you really need to work on these old cars yourself to make owning one worth while. At this point I'd stop all work and get the car out of their ASAP. You are already up to $20k which is insane IMHO. You are 60% of the way to a new C class!

The dealer is raping you!

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200