I screwed up a 190E post the other night & managed to turn a head or two the wrong way. Let's see if I can redeem myself.
Just browsed an MB history manual and your car has an M102 engine if I'm not mistaken.
According to the photo, it's 2/3s of an M103 engine(6 cyl)......looks similar.
- I see you're in Okla - still warm. Given that yours is a '85 model, I'd go with 10W-40 oil...any good brand. Forget synthetic. I've managed to take too many cars beyond 200K without it and for alot less money.
- Have you located the oil filter and engine drain plug? Not sure if your filter is a screw-on-from-the-top like mine. Alot of MBs like yours/mine use a 13mm to remove oil drain plug.
You may possibly have a large plastic shroud underneath the car that will need to be removed if you're going to "drain" the oil from the bottom. If so, remove it and look for drain plug on oil pan.
Drain oil/replace oil filter. Coat filter gasket with oil before installing. Screw on hand tight, then give the filter just a tiny snug with an oil filter wrench. Replace oil drain plug. Fill engine with specified amount of oil(see owners manual).