4matic repair will make you and the mechanic wince with pain. The later models look nice with their body kit and headlamps and sit lower too, Their dashboard is also slightly different (more wood). But they are heavily padded everywhere to insulate from noise.
The problems with the late W124 were bad wiring insulation that breaks down after 10 years or so (the engine room one) - the rest remains good. Some A/C cars had bad evaporators from the factory that leak (replacing them requires removal of the entire dashboard, the wiper etc.. Its not as easy as a corolla.
Otherwise the car is good - but bear in mind that at this age you will want to check all rubber parts under the car (any model W124), Its got a lot of bushes in the rear, 5 links a side (10 bushes), one bearing bush each side, 4 sudframe bushes, 3 differntial bushes. When all are in good condition the car works like it should (firm yet supple ride), if they are bad - it would ride like a bad maintained mehran.
The front is pretty simple, but only get it aligned by someone who has the additional tools required to align this car. Its not just simple tow adjustment, in this car, caster, camber and toe are adjustable. - The steering box needs to be locked first then a road force simulating bar installed between the front wheels. Then the technician should follow the exact chassis spec alignment, e.g. E200 and E420 have different alignment.