bequeathed 1st diesel benz, what now?

My father-in-law passed along a beautiful 82 300sd with 167,000 miles. He is the original owner and maintained it scrupulously (I've got all the records). He says it has lost a bit of power over the years, but it gets going okay when it is warm. It trucked up some long freeway grades (from California to Seattle) at 70mph, no problem -- could have gone 80-85 at least. It got 26 mpg on the long trip at a consistent 70mph on the cruise.

It burns a lot of oil -- up to a quart a tank of 20-50 if cruising at higher rpms. But it still goes pretty good and starts without complaint. Apparently it leaks just a little bit of oil at some blow-by or recirculation pipe (on the block beneath the turbo), but I'm thinking it is the ring or valves or something like that. Is there anything I can do about the oil consumption? Should I be worried?

What are the most important things I can do to maintain an older diesel? What is important to know?

Please help me keep this truly wonderful car running for a few more years

many thanks and happy new year