most expensive repair?

You got a deal on the A/C, most places on average charge $2500 at least. Mine was $3300, but they also replaced the heater core, dryer and receiver, but that may be the usual thing everyone has done while the instrument panel is out.

I would say after that, the wiring harnesses.

I just went back and looked through my 202 pages of service records... The highest I seen was indeed my A/C repairs and it was actually $3144.00. The next one down was the engine wiring harness and some other repairs mixed in, which made that bill around $1800... also on that invoice it stated where the "actuator" was replaced (part alone was $768). Not even sure what the actuator is. lol.

Also most recently the PO had the ignition wires replaced, spark plugs as well as many other ignition components and it was around $800. Valve cover gaskets in April, that was $500 and some change.

Definitely not cheap cars to service and when I think about it sometimes, I ask myself why didnt I buy another W126 S-Class or a Honda Accord, but I love this car. LOL.