Very concise advise dispensed here. Do look into the comments on the oil.
I would be particular on the chasis, so tat if you do decide to invest in this marque, you'd do so knowing that your chasis will need minimum attention (and maximum enjoyment).
Check for any waves along the bodyline just to be sure its really accident free, and then the rust (if any) along the bottom of the floor mat, boot cover, windscreen/backscreen hinges, on bonnet, and particularly right beneath the door mounting/sill.
For a concise illustration of most problems encountered by W126s, do make a dive into http://www.w126.com
Fuel consumption is excellent for long haul drives, but horrid for short distance/traffic crawls.
Tranny change a little rough but on the whole, a durable car.
Its one great car to be having.