You are talking seats clean, or oil pan clean? With over 20 years old car, 99.9% of the time there will be issues. Parts will be more expensive than for W123 and gasoline engine will be shorter lived. I am not sure that would be right change.
IMHO the W210 are the best value right now. You can find high miler for $3000 while good one for 5000. Those cars do have some sensors and cosmetic issues but engines and transmissions seems to be bulletproof.
Than coming from W123 it would be like dropping the rotary phone and picking up cellular.
I mean that all around it looks like a pretty well maintained car. Of course, I will never buy a car without test driving it and having my brother look it over (he is a mechanic). But it is in a very reasonable price range for me and I think it's worth taking a look at.
1987 Mercedes-Benz 190 E 2.3, $2,350 - Cars.com
My main concern with a W210 would be the maintainance/insurance prices. I've heard that the only true bulletproof Benzes ended in the late 80s, which is why I tend to lean a little more towards something like a 190e or 300e. They're easier to find with low mileage and still look pretty nice cosmetically.