It does sound like a fuel delivery problem. I would be careful not to leave out the possiblity that it may be a combination of issues rather than just one. That said, if you are on you original injectors, replacing them would be logical at this point. Its a testament to the fact that you only use high-octane fuel that you've lasted this long. All new seals, injectors and breathers should be under $300 and just take an afternoon (I'll be doing the job tomorrow, so I'll let you know). You should also replace your fuel filter ($20) if you haven't already.
In my case I lucked out, the firm I work for had an old ultrasonic cleaner than no one has used for years. It was used for drafting pens and so on. I guess some people clean jewelry in it but thats about all. Anyway, after I pull mine tomorrow I'm going to leave them in there for a couple of hours and then blow them out with carb cleaner. I was mostly worried about my leaky seals but this certainly can't hurt.
1988 420SEL 170K