Mercedes ML 320 TDI Issues

[nyko46]

This past year my son bought an used 2007 Mercedes ML320 TDI with 150K and drove it 20K sinc the date of purchase.
He is a very careful person with his cars but is extremely disappointed with the number of problems that this car is giving to him. According to the seller, a private dealer paperwork, this car was carefully maintained and serviced by MB dealers.
In only one year this car had four major problems taken a good amount of money in repairs performed by a local shop repair. The shop only work with European cars.
Here is the problems that this car already had:
1- Turbo over boost code. Mechanic replaced the turbo which was with a waste gate valve broken. Spent around $ 3K
2- Exhaust Filter clogged. Mechanic try to clean but finally had to replaced the exhaust filter. Spent around $ 1.5K
3- New issue: Air Suspension not working, car have a rough ride. Not yet fixed.
4- New issue: Transmission does not shift from first gear. Need to stop the car and start again. Not yet repaired.
The reason why he bough this Diesel car is because it was more economic going and coming from his work.
He and I will appreciate if someone share with us if there are some bad historic about this car year of manufacturing or any other possible reason for so many issues on this car.
Thanks.