My 84 528e sat for 5 years and it started after two cranks after installing new plugs. I also had to run injector cleaner 3-4 times untill things smoothed out. The only major thing that happened is the head gasket failed after 800 miles or so. My BMW guy called it, he said that the gaskets rot when the car sits and if you get to 1k miles your home free. I didn't make it. When we took the head off the head surface was pitted badly so I replaced the head, gasket, water pump and timing belt. The only thing I regret is not replacing the front seal while in there.