Our 91 300E (2315k miles) uses oil, but it is from the front cover seal. I slowed that seeping by trying the "high mileage oil" MaxLife from Valvoline. It improved the oil consumption (leak).
It is my understanding that in 1990 or 1991 the valve guides and valve stem seals were improved. I also believe that in the last ten years oils have very much improved so it doesn't surprise me that your '87 with 170k miles is doing well.
I just started using Mobil 1 15w-50 in the project '87 190e. The car seems to really like this oil. It starts easily and even in our 100+ degree days, never gets too hot. We also noticed the engine to be much smoother. This I can't explain but it is so.
I have been following the Mercedes service recommendations carefully. I also have flushed the power steering fluid and change its filter. All the cars have synthetic AFT and differential lubes.
Enjoy your drive,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)