it's very unrealiable, i know a shitload of guys who own these cars, and their wallets get skinny very quick. You have to keep the car in tip-f@cking-top shape to make it reliable, and to do that you need to have spare cash. 2003 540i is abit better, they've improved on some issues so it is definately more reliable than a 97. But like other guys said, get couple of sets of valve cover gaskets for the next year, they usually last 4-5 months before they leak.
1990 M5 Euro
You wash your car like it was your firstborn child, you tend to its needs like it was your own body, you protect it like it's your family, then you drive it like you stole it