You got a good one, and they are lovely cars when everythings works.
Just clean and wax the filler door area unless you actually think it is rust. In that case, it needs some conversion (etching) primer and some new paint.
Valve adjust interval is 15,000 or 30,000 miles. Good thing is that they don't wear much, unless the oiler tube fittings get broken, in which case it is a camshaft rather than valves!
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!