All '85s are not trap oxidizer models....only California versions.....Federal versions have regular air cleaner housing with oil blowby hose and drain.

Having done a lot of repairs on my car, and having followed MBZ chat sites for a few years, I know of no real quirks with the 85 as compared to others. As mentioned in previous response, there are some minor differences/upgrades pertaining vacuum system, transmission, cruise, but not major ones.

It sounds like a good vehicle...an 85 with 110,000 miles is a find.....hopefully it has not been stored for long periods.

The main thing I would try to verify is if regular oil changes and valve clearance adjustments had been done...if so, there is not much that could have gone wrong with upper (valves, head) or lower end (pistons, rings,etc.).

There are a lot of 123 diesels for sale that have had a valve job (or need one) at 100,000 miles or so....only because the car was neglected and valve clearances were not done.

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)