...of buying an old model.? The car is a 1985, with 193,000 miles on it. My understanding is that high mileage is no issue for a Benz, but would feel better about making the purchase if I had a few independent opinions. (Also, I did run a CarFax search on the VIN and it came up clean.)

Try a good diy site with parts mercedessource.com
I learned alot from them performanceparts4benz is good but slow.There are 2 things in that engine that need tending if no records.One upgrade timing chain to double chain,and some plastic parts under valve cover.As with all Benz engines they can last a lifetime.

These are truly beautiful cars, but as with all Mercedes Benz models they are expensive to repair.
The R107 model was the longest run for Mercedes Vehicles (17 years) so parts continue to be readily available.
The best bet you have is to inspect the maintainance records closely and have the car inspected by a certified Mercedes mechanic.