Well after all this time i cannot resist and have to jump in.
W126 worth matters alot depending on car to car and specs.
Probably a very nicely kept original sel500 or 560 would be priceless but should be around 25 lacks.
And all other petrol powered spotless ones should be around 12 lacks.
Coming towards manual transmission 280 or something similar should be around 9 max.
Finally diesel and avg condition 280's are below 9. Can be 9 or can be as low as 2 to 3 lacks.
Do keep in mind its really hard to sell a w140 these days. 320 etc hardly sell around 12-17 lacks. And if there is a s500 or 600 out there no one will sell it.
Now coming todwards this particular 280se(i will not discuss the price)
A Benz enthusiast will never buy it because of the toyota engine and its over all mix breed features.
And majority of other guys will not get a thirsty car(Even if its giving 8/liter its thirsty for them)
Thirdly other guys they already have a japanese with v8 swaps.
So buyer for this car is very very rare.
No doubt car is good etc and other facts but Market aspects do matter.
But fact will be fact that is a w126 which is completely showered with toyota engine. :p.