I agree entirely with what Martin said although I would suggest one thing. If you're going to DIY, first replace your injectors (because you really aught to with that kind of milage), that'll run you about $250 in parts. Along with that replace your fuel filter ($20) and your check valve ($11). See where that gets you, if you running well then you are all set. This is what I did.
Otherwise the accumulator is the most likely suspect as the fuel pumps seem to run forever. Its about $120 or so and you wouldn't want to replace it if you don't need to.
Also, do a few searchs on 'fuel pressure leakdown' and 'vapor lock'. Read a bunch of posts and look at what stevebfl has to say in particular. Although I didn't have a hot starting problem (vapor lock) after reading his discriptions I realized that my case was almost classic fuel pressure loss.
Also, take the time to do Kbowers fuel distributor test, pray this isn't your problem, its big bucks.
1988 420SEL 170K