Recently purchased 97 s 320w, 75,000 miles. Service records indicate replacement of cylinder head, instument cluster and oxygen sensor. What should I be looking for next? What about A/C evaporator?

A/C evaporator is definitely an issue on the W140. That doesn't mean that yours is going to fail. Why was the cylinder head replaced? Was it simply refurbished for a head gasket replacement? I would start off by going through serving records to see when fluids were last changed, especially the transmission fluid.

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1989 300CE

Car fax indicates cylinder head replaced at 20,723 miles. Does not say why. Also drive shaft flex discs replaced at 31,000m. Service book is complete to 69,000 miles indicating all factory recommended mtc. items complete. Is transmission fluid flush a recommended service item?

The M104 engine does have tendency to eventually need headgasket replacement. Not sure why the cylinder head would need replacement with that few miles unless it experienced some sort of serious failure. The transmission fluid should be replaced at the regular intervals as indicated in your service book. You can drain a good portion of the fluid if your transmission still has a drain on the torque converter. I know Mercedes changed the guidelines in the late 1990s to a "lifetime fluid" but they eventually went back to fixed intervals.

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1989 300CE

I will be taking it in for 75k service in near future to the same dealer that performed all previous mtc. I will see how specific they can be c/o cylinder head. Any other ?? I should be asking them?

FWIW, I just had all the drivetrain fluids done on my "new" W211 with almost 70k miles. I don't believe in "lifetime fluids."