At 205K on that engine (M103) I'd expect that there has been a valve job done in the past (generally around 150K) and not just valve seals. Some owners try to cheap out by just doing valve seals. The 103 engine is notorious for oil consumption beginning around 150K. Also check that a timing chain was put in when the valve job was done. The rest of the car is equally as bulletproof but engine maintenance is a big factor with 300Es. Otherwise, $2,500 is pretty fair if the car is decent.

You might also see if the suspension has been checked out.

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Regards,
Aaron