Your car has the M62TUB35 engine, which uses an Aluminum alloy with Alusil in it instead of Nikasil. What this means is that in terms of teh engine, you should be fine. BMW had serious issues with Nikasil blocks before it decided to abandon them and use Alusil alloy instead.
How many km on the odometer? These cars last for a long time and even their automatic transmissions tend to last for a long while (a buddy of mine had his auto transmission on a 5er go for 450,000 km!). One thing about the transmission: BMW claims that their cars come filled with "life-time" transmision fluid. I don't trust that. The fluid will deteriorate over time, so your transmission will run better and for longer if you replace the fluid as soon as you get it (unless it has been replaced recently). You want to replace the fluid around teh 120,000 to 150,000 km mark. If it over that... come back and ask. Some people think once it reaches that point, you're better off just leaving things alone.
The best advice we can give you is that you take the car to a mechanic. I know it may feel like lost money if you decide not to buy the car, but it is important t know what kind of shape the car is in.
Hopefully the current/previous owner(s) have kept maintenance records. Those are worth gold when buying a used car.
I know I threw a lot of info at you. I probably brought up more questions tahn I answered, but I hope this helps.
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