Am I asking for too much?

Research what it would cost to repair the mechanical issue with the car, and what you could get for it, then.

When I was selling off my vehicles, I found that if I made the repairs to the mechanical issues, I could actually recapture about 1.3 times the money it cost for the repairs. I suppose many people who aren't mechanically inclined don't mind paying extra for a car in good mechanical condition. I had similar experiences with about 6 vehicles that I sold.