If you end up looking at an import 560SEC with the 220kW ECE spec engine, keep in mind that they have a rare and expensive 8-pin EZL ignition module... very expensive to replace and hard to find. Having said this, if the coil, leads and distributor cap/rotor are kept in top shape, then there is little concern.
The rust under the rear window is indeed a huge problem on the SEC (and even the W126 as a whole). Look for poor quality repair, and I stress the importance of looking up underneath through the circular holes for peeling paint and rust holes.
Also, those seat belt arms are often broken, so make sure they work.
The best thing about these cars is that if the CIS computer fails, you can still drive the car normally, and probably won't notice other than fuel economy reduction.
The front suspension lower joints and brake support ball joints are usually stuffed too, so you can count on needing to replace them on most cars too.
As for the timing chain... if there's no history of it being renewed, and more importantly the plastic guides and tensioner, then it will need to be done immediately, along with the camshaft oiler fittings (only a few dollars for a set). This is an easy DIY job in my opinion.
Watch for worn cam lobes due to poor lubrication, which is often the result of the loose plastic fittings mentioned above.
Otherwise... they're great cars when well sorted!
Tim
