Check the windshield seals for dry rotting and cracks. If they are cracked, there is probably rust underneath, could be significant enough to need some serious restoration or simply walk away (I know I'm late to the thread).
Suspension bushings, voltage regulator, rocker panel rust, spare tire well rust, window regulators.
Also, you want to ensure the heater blower in the dash works. Mercedes bought a fan, then designed the car around it. Replacing it is an unholy pain in the butt, necessitating removal of the center console under the dash, all the controls, the heater core, a bunch of shrouds and tubes for the vents, and of course, the fan itself.
I love my 220D so much more than my old W123 300D. It just feels like a nicer car in my opinion. And mine is a zero-option car, no power anything. I'm using my abs, and arms when parallel parking. This is something that ensures that I keep tire pressure up too.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson