My dad owns a 1989 750iL and it has seen its better days. It was used alot though. As far as maintenence goes..it is like any other BMW...you may not ever have a real problem with it, and it may also drive you crazy. He had moderate problems with it. He bought it when it was like 4 years old. He had some problems with the A/C. He spent $4800 on it and it still never worked. The exterior door handle broke off too, lol. But over all it was a great car, really good acceleration, but depends on if this guy has a deep wallet in the case a major problem comes up. If a problem ever does exist....we still have the car and we may be able to give/sell some parts to him. Hope this answers your Q.
I'll ask my dad if he has any comments to add to help him.