The stock exhaust was rusted badly when I just bought the car and had quite a lot of holes in it. The smell and sound of exhaust gasses were quite noticeable inside the car, so I had to replace all the exhaust further than catalyst. Paid ~ 200€ for a new one.
Oxygen sensor failed at 214.500 km which caused unstable engine running. Payed about 60€ for a new NGK sensor. The original one would have cost 230€.
Changed front shock absorbers at 219.000 km.
I wasn't able to turn the ignition key to start the engine one evening and discovered that the ignition lock (not sure what it's called in English) is stuck. I managed to repair the fault myself, however.
The thermostat failed at 222.000 km causing the engine Would cost about 15€ for a new one (Wahler). I'm still considering whether to change it by myself or at the service station.
Other than that just the ordinary wear and tear.
When I decided to buy a car, I already knew that it would be a BMW 5 series. And I must say that I'm not disappointed with it. It's a fantastic car! No other car has that drivers soul like a BMW. And 5 series E34 is one of the best cars the company has ever made.
The interior is quite comfortable, seats have a good side support while cornering and everything is organized very well and easy to reach. You feel like inside a German World War II plane in this car. Fantastic feeling!
There's not too much room for legs at the rear seat for a business sedan, but it's OK as long as there's no more than 2 people sitting at the rear. There's plenty of space at the front. The trunk is quite roomy too.
The M50 inline 6 engine is the best! It's a bit underpowered at low revs, but after 3000-3500rpm the acceleration is awesome! 150 h.p. is just enough for this sedan, but I think that 525i with it's 192 h.p. is an optimal choise. M50's with VANOS that came from september 1992 should be even better.
Handling is excellent, the car handles like on tramway rails. Steering is balanced very well: the slower you drive the more responsive it is, so you always have a good feeling of the car. But you should take care and drive carefully during winter on slippery roads because of the rear wheel drive. Good winter tires are recommended.
Maintenance of this car is quite expensive: the majority of spare parts cost more than on other vehicles, but I think it's worth it.
I can't say that the fuel economy is excellent, but it's adequate. It "eats" about 14 liters per 100 km in town and about 8 liters on the highway.
The other good point is that it's not too complicated to do a lot a repairs and maintenance jobs by yourself. You would spare quite a lot of money doing it yourself. But if you don't feel confident in your mechanics abilities - DON'T.
The car is quite reliable, though sometimes I wish it to make a bit less "surprises".
Overall it's a beautiful, comfortable, fast and serious sedan. A real joy to drive.