engine usually not the problem
the problem is poor maintenance, improper modification, causing electronic issue, spare part wear out, sensor rosak, etc

for conti car like merc, audi, bmw, the car need to proper maintaining since the beginning
so i will recommend get a new 1 instead of used, bcos msian is calculative, when come to maintenance, they will always choose the cheapest or even try to avoid...

the cost to replaced/fixed is similar to get a new one...