Faults:

Ignition module broken (+- 500 euro second hand).

Air conditioning leaks.

Central locking not working and some other things related to the vacuum pump.

Shock absorbers had to be replaced (500 euro second hand).

Oil leaks +- 1l per 1000 km.

Some other smaller things I forget.

General Comments:

Most impressive car I have ever driven (and probably ever will) and also the most expensive: spent +5000 euros on maintenance in 2 years (and I go to a garage that doesn't charge Mercedes maintenance prices).

Still love this car by the way. When I arrive home, I often wish the road was longer...

Not easy for city driving because it is 5m 11cm long and wider than an ordinary car.

Uses 16l/100km on average (LPG).

Oh yes, it pulls a bit to the right. Tried everything. Some say it is normal for old Mercedes models, because of the roads. That they used to align them a bit to the left in the garage. Nowadays these things are regulated electronically.

Conclusion: great hobby if you have a great budget. If you don't, I recommend you maybe buy one just for the experience and sell it again soon (what many people do once they realize the costs of the parts -> they are not so easy to find second hand. Also most mechanics don't really know how this car works: it is extremely complex to work on).

The person before me got the automatic transmission fixed, and the wiring harness is also something to check before buying. Air con evaporator can break -> costs 2000 euro because the entire dashboard has to be taken off.

There's a great forum on Facebook where owners help each other (Mercedes S Klasse W140 group -> no I am not the owner of the group, but I recommend you to join, because I have been helped a lot with my questions).