Take a look at the buyer's guide for the W126 SEC coupes fro a run down on what to look for on the chassis before you buy.
www.mbcoupes.com (The buyers guide)
It is not so new, but fairly comprehensive, and well regarded on the net. I co wrote it back in1998 so nevermind about the prices mentioned.
The 300SE is the sexy looking close coupled body. Astal Silver with a black interior is a very, very nice looking set up.
The 177 hp inline six won't accellerate from a stop or in passing gear like the 560, but on the other hand (if that matters) it makes politer sounds at the gas trough, and it will cruise on the highway at speed just as well as the rest of the 560 cars.
The six cylinder motor is a very good one, one of Mercedes' better efforts.
Actually, they are quite peppy around town, because of the rear axle ratio, and for a big car like that the handle amazingly well and have in the SE body style a great tuning ratio, and are quite nimble in parking and tight turning situations in big cities and close quarters.
They are also engineered and crafted to a cost no object standard of build quality and reliability.
Plus, you are looking at the last production year of a great body, always a plus, you have all the latest interior, exterior refinements that you could get.
If I were you, I would definately buy it, if it passes PPI and the faults are considered in the final price paid.
And in the end, you'd have an appealing, elegant, safe, comfortable, durable, car for a fraction of its cost new.
In ten years what you paid for it today, won't mean a thing.
They are legendary, beautiful, cars that you could, with reasonable care, keep forever to use and enjoy.