US-model 240D automatic, with rust, Michigan title = $1000.00 too $2500.00 if it has a good engine / drive train.
Rust + bad valves + interior wear + paint wear = reduced value.
240D is not a hot sale vehicle, ask other forum members.

As I stated, if you like it, put the money into repair and keep it.

Frank told you what is wrong, you seem to be rejecting his diagnosis.
I can do nothing but repeat what Frank said.
Further testing is a waste of time, money and energy, until the valves are repaired...