W124s are great cars, although be careful of 1986/1987 models. The first years of production were not kind at all to this series. I owned an 1986 300TE (Euro version) which had several jobs performed by the dealer (most under warranty) because of upgrades or modifications that were later issued (mostly between 1987-88)by the factory. The worst and most impressive repair was done in 1996, due to several miniature cracks on the rear axle.
After research, I found out the 86/87's tended to develop this problem after 80,000 kms. Also, I found out that Mercedes-Benz provides a 10-year warranty on the chassis, so I applied my rights on the dealer and the problem was fix (about a $3,500 job including parts and labor). The cracks were discovered during a rutine x-ray exam which my local dealer performs on all cars reaching 100,000 Kms.
On my 300TE the A/C always worked perfectly, although do not expect it to be as ice-cold as a luxury Japanese or American car.
Other regular problems on 86/87s were power window failures, vacuum assisted problems (door locks and headlight aim adjustable angle -Euro versions-). Models 200/230E were a nightmare come true because of the distribuitor chain.
Most of these problems were fixed on production lines after April of 1988.
Good luck with your new car!